Foolish Assumptions
First, I assume that you know enough about computers to understand terms
like files, directories, path names, and other basic operating system concepts.
I assume that when I tell you to put a file in a specific directory, you know how
to do that.
Next, I assume that you know how to create files. You need to know how to
create a file and edit it by using a basic editor, such as Notepad in Windows.
You need to know how to save the file, copy it, and move it around.
I assume that you are using an operating system that PHP runs on, which
included almost every operating system. Your operating system needs to be
reasonably current. For example, Windows 95 is too old, as is Mac OS 9. Even
Windows 98 is a little old, although some people do run PHP on it.
If you’re using PHP for the Web, you need to use HTML (HyperText Markup
Language) statements. I assume that you know HTML. Consequently, although
I use HTML in many examples, I do not explain the HTML. If you need to use
PHP for a Web site and you do not have an HTML background, I suggest that
you first read a book on HTML — such as HTML 4 For Dummies, 4th Edition,
by Ed Tittel and Natanya Pitts, or HTML 4 For Dummies, Quick Reference, 2nd
Edition, by Deborah S. Ray and Eric J. Ray (both by Wiley Publishing, Inc.)
Then build some practice Web pages before you start this book. However, if
you’re the impatient type, I won’t tell you that it’s impossible to proceed without
knowing HTML. You may be able to glean enough HTML from this book
to build your particular Web site. If you choose to proceed without knowing
HTML, I would suggest that you have an HTML book by your side to assist
you when you need to figure out some HTML that isn’t explained in this book.
Also for PHP for the Web users, I assume that you have created at least a static
Web page, probably one or more static Web sites. I assume that you know
where you need to put files so that your Web pages are available to your Web
site users and that you know how to put the files in the appropriate place by
using copy, ftp, and so on.
I do not assume that you know anything at all about writing computer programs
in any language. This introductory book provides the needed instructions
for anyone to write PHP scripts. So, if this is your first programming
language, you should be fine. If you have a background in another programming
language, particularly C, you may find this book to be a quick reference
to learning how to do things in PHP. However, those who have no background
in programming will find all the information that they need.
3 Introduction
How This Book Is Organized
This book is divided into six parts. The content ranges from an introduction
to PHP basics to common applications for PHP.
Part I: Say Hello to the PHP
Scripting Language
This part provides an overview of PHP, including how it works and its many
uses. You discover how to set up your environment for using PHP. Finally, this
part shows you how to create your first PHP program.
Part II: Variables and Data
Variables are the fundamental feature of PHP. This section shows you how to
create variables and use them. It also describes the kind of data that you can
store in a variable as well as how to handle the various types of data. Then,
you find out how to create and use complex variables called arrays.
Part III: Basic PHP Programming
This part shows you how to program PHP scripts. You find out about the basic
features of PHP and the details of how to use them to create your scripts. This
part also introduces you to object-oriented programming.
Part IV: Common PHP Applications
Part IV provides the techniques needed to write scripts for the most common
PHP applications. You find out how to write scripts for use in your Web site,
such as how to display HTML forms and how to process information that users
type into forms. You find out how to use PHP to interact with databases. Using
PHP to perform system tasks, such as writing files on your hard disk and executing
operating system commands, is also described.
4 PHP 5 For Dummies
Part V: The Part of Tens
This part provides some useful lists of things to do and not do when writing
PHP scripts, as well as a listing of PHP resources.
Part VI: Appendixes
This part provides detailed instructions for installing PHP for those who need
to install it themselves. Appendix B is a list of functions available in PHP,
intended to be a useful reference while you write your scripts.
Icons Used in This Book
Icons are provided to help you identify information in this book. The following
icons point out types of information for your notice.
Tips provide extra information for a specific purpose. Tips can save you time
and effort, so they’re worth checking out.
This icon is a Post-It note of sorts, highlighting information that’s worth committing
to memory.
You should always read and pay attention to warnings. Warnings emphasize
actions that you must take or must avoid to prevent dire consequences.
This icon flags information and techniques that are more technical than other
sections of the book. The information here can be interesting and helpful, but
you don’t need to understand it to use the information in the book.
5 Introduction
6 PHP 5 For Dummies
Part I
Say Hello to the
PHP Scripting
Language
In this part . . .
Iprovide an overview of PHP. I describe PHP, how it
works, and what it is useful for. After describing your
tools, I show you how to set up your working environment.
I also present options for accessing PHP and point
out what to look for in each environment.
After describing the tools and options for the development
environment, I provide an overview of the development
process. I show you how to write your first script
and discuss a few simple output statements.
Chapter 1
Getting to Know PHP
In This Chapter
Taking a look at PHP
Understanding how PHP works
Understanding PHP as open source software
So, you want to get to know PHP. Perhaps this is your first adventure in
programming, and you chose PHP because your techie friend told you
it’s easy to understand. Well, your friend is right. PHP is one of the easiest
programming languages to understand. The developers of PHP strive constantly
to keep it easy to use.
Perhaps you already know how to program in another language. You’ve
decided to study PHP because it’s the best language for your new Web application
project. It’s a good decision because PHP is well suited for writing
dynamic Web applications. PHP is easy to get started with, but it also has
many advanced features for seasoned programmers. If you know C, you
have a great head start because PHP syntax is similar to C syntax.
In this chapter, I discuss what PHP is, what it can do, and how it does it.
Getting Familiar with PHP
PHP is a widely used open source, general-purpose scripting language. It was
originally designed for use in Web site development. In fact, PHP started life
as Personal Home Page tools, developed by Rasmus Lerdorf to assist users
with Web page tasks. PHP proved so useful and popular, it rapidly grew to
become the full-featured language that it is today, acquiring the name PHP
Hypertext Preprocessor along the way to represent its expanded abilities —
processing Web pages before they’re displayed.
The popularity of PHP continues to grow rapidly because of its many
advantages:
It’s fast: On Web sites, because it is embedded in HTML code, the time to
process and load a Web page is short.
It’s free: PHP is proof that free lunches do exist and that you can get
more than you paid for.
It’s easy to use: The syntax is simple and easy to understand and use,
even for non-programmers. For use in Web sites, PHP code is designed
to be included easily in an HTML file.
It’s versatile: PHP runs on a wide variety of operating systems —
Windows, Linux, Mac OS, and most varieties of Unix.
Technical support is widely available: You can join one of several
e-mail discussion lists offered on the PHP Web site (www.php.net),
which cover topics such as general PHP, PHP on Windows, or databases
and PHP. In addition, a Web interface to the discussion lists is available
at news.php.net, where you can browse or search the messages.
It’s secure: As long as your scripts are designed correctly, the user does
not see the PHP code.
It’s customizable: The open source license allows programmers to
modify the PHP software, adding or modifying features as needed to fit
their own environments. PHP provides significant control over the environment,
reducing chances of failure.
Considering the Various Uses for PHP
PHP is a general-purpose language that can be used to write general-purpose
scripts. Scripts are computer files containing instructions in the PHP language
that tell the computer to do things, such as display Hello on the screen or
store some specified data in a database. Most scripts contain a series of
instructions that can accomplish tasks from designing Web pages to navigating
your file system. Because PHP began life on the Web, it has many features
that are particularly well suited for use in scripts that create dynamic Web
pages. Currently, you find PHP most often hard at work in Web pages, but its
use for other purposes is growing.
PHP is very popular for Web sites. According to the PHP Web site (www.php.
net/usage.php), over 11 million domains are using PHP. Yahoo!, which is
probably the world’s most visited site, recently decided to change from its
own proprietary language to PHP.
10 Part I: Say Hello to the PHP Scripting Language
Using PHP for Web applications
In the beginning, Web pages were static — they just presented documents.
Users went to Web sites to read information. Documents were linked together
so that users could easily find the information they sought, but the Web pages
didn’t change. Every user who arrived at a Web page saw the same thing.
Soon Web page developers wanted to do more. They wanted to interact with
visitors, collect information from users, and provide Web pages that were
customized for individuals. Several languages have developed that can be
used to make Web sites dynamic. PHP is one of the most successful of these
languages, evolving quickly to become more and more useful and rapidly
growing in popularity.
PHP is a server-side scripting language, which means that the scripts are executed
on the server (the computer where the Web site is located). This is different
than JavaScript, another popular language for dynamic Web sites. JavaScript
is executed by the browser, on the user’s computer. Thus, JavaScript is a clientside
language. Web servers and the interaction between servers and clients are
discussed in the section “PHP for the Web,” later in this chapter.
Because PHP scripts execute on the server, PHP can dynamically create the
HTML code that generates the Web page, which allows individual users to
see customized Web pages. Web page visitors see the output from scripts,
but not the scripts themselves.
PHP has many features designed specifically for use in Web sites, including
the following:
Interact with HTML forms: PHP can display an HTML form and process
the information that the user types in.
Communicate with databases: PHP can interact with databases to store
information from the user or retrieve information that is displayed to
the user.
Generate secure Web pages: PHP allows the developer to create secure
Web pages that require users to enter a valid username and password
before seeing the Web page content.
PHP features make these and many other Web page tasks easy.
PHP is only server-side, meaning it can’t interact directly with the user’s computer.
That means PHP can’t initiate actions based on the status of the user’s
computer, such as mouse actions or screen size. Therefore, PHP alone can’t
produce some popular effects, such as navigation menus that drop down or
change color. On the other hand, JavaScript, a client-side scripting language,
11 Chapter 1: Getting to Know PHP
can’t access the server, limiting its possibilities. For example, you can’t use
JavaScript to store data on the server or retrieve data from the server. But
wait! You don’t have to choose. You can use JavaScript and PHP together to
produce Web pages that neither can produce alone. See Chapter 11 for details
on using JavaScript and PHP together.
Using PHP for database applications
PHP is particularly strong in its ability to interact with databases. PHP supports
pretty much every database you’ve ever heard of and some you haven’t.
PHP handles connecting to the database and communicating with it, so you
don’t need to know the technical details for connecting to a database or for
exchanging messages with it. You tell PHP the name of the database and
where it is, and PHP handles the details. It connects to the database, passes
your instructions to the database, and returns the database response to you.
Major databases currently supported by PHP include the following:
dBASE
Informix
Ingres
Microsoft SQL Server
mSQL
MySQL
Oracle
PostgreSQL
Sybase
PHP supports other databases as well, such as filePro, FrontBase, and
InterBase. In addition, PHP supports ODBC (Open Database Connectivity),
a standard that allows you to communicate with even more databases, such
as Access and IBM DB2.
PHP works well for a database-driven Web site. PHP scripts in the Web site
can store data in and retrieve data from any supported database. PHP also
can interact with supported databases outside a Web environment. Database
use is one of PHP’s best features.
12 Part I: Say Hello to the PHP Scripting Language
Using PHP with your file system
PHP can interact with your file system — the directories and files that are on
your local hard disk or on other computers accessible over a network. PHP can
write into a file on your file system, creating the file if it doesn’t exist, and can
read the contents from files. It can also create directories, copy files, rename
files, delete files, change file attributes, and perform many other file system
tasks. PHP allows you to perform almost any task related to your file system.
Many Web sites need to interact directly with the file system. For example,
a Web application may save information temporarily in a file rather than in a
database, or may need to read information from a file.
System administrative and maintenance scripts frequently need to interact
with the file system. For example, you may want to use a PHP script to back
up files, to clean out directories, or to process text files by reformatting their
contents. PHP can perform these tasks quite well.
Using PHP for system commands
PHP can interact with your operating system to perform any task the operating
system can perform. You can execute an operating system command and
receive the output. For example, you can execute a dir or ls command (to
list the files in your directory) from PHP and receive the list of filenames that
the dir/ls command produces.
The ability to execute system commands is often useful for system administrative
and maintenance tasks. For example, you may want to clean up a
directory by deleting files with a particular extension. You can use a system
command to get a list of files in a directory and then identify and delete the
files with the unwanted extension.
The ability to execute system commands includes the ability to run any other
program on the system. Thus, you can run programs in other languages from
PHP and make use of the output. Aren’t you relieved that you don’t have to
rewrite all those programs you’re using now? You can run Perl, C, shell scripts,
or any other language programs from PHP. New PHP programs can add functionality
to your system tools, without requiring you to spend time rewriting
existing tools.
13 Chapter 1: Getting to Know PHP
Understanding How PHP Works
PHP is a high-level language, which means that it’s human-friendly, similar to
English. Because your computer doesn’t understand English, you use PHP
to communicate, and the PHP interpreter converts the language in your PHP
script to language the computer can understand. The computer then follows
your instructions, passed to it by the interpreter.
The PHP interpreter comes in two flavors, one for use with Web sites and one
that you run from the command line, independent of the Web. You can install
either or both.
PHP as a general-purpose language
When you use PHP as a general-purpose scripting language, you install PHP
CLI, the version of PHP developed for this purpose. You access the PHP interpreter
from the command line to run your PHP script. The process is similar
to other languages, such as Perl or C. For the lowdown on running scripts
using PHP CLI, check out Chapter 3.
14 Part I: Say Hello to the PHP Scripting Language
How the World Wide Web works
It’s helpful to understand a little about how the
World Wide Web (WWW) works. The Web is a
network of computers that offer Web pages.
Millions of Web sites are on the Web. To enable
Web surfers to find the Web sites they want to
visit, each Web page has an address, called a
URL. This includes the Web site’s domain name
and the filename, such as www.mycompany.
com/welcome.html. When Web surfers want
to visit a Web page, they type the URL into their
Web browsers. The following process is set in
motion:
1. The Web browser sends a message out
onto the Web, requesting the Web page.
2. The message is sent to the computer at the
address specified in the URL.
3. The Web server software on the addressed
computer receives the message.
4. The Web server searches for the requested
HTML file.
5. The Web server finds the requested file and
sends the file to the Web browser that
requested it. (If it can’t find the file, it sends
a message to the browser saying that it
couldn’t find the file.)
6. The Web browser displays the Web page
based on the HTML code it received.
PHP for the Web
When used on your Web site, PHP works in partnership with your Web server.
Every Web site requires a Web server. The Web sever is the software that delivers
your Web pages to the world. The PHP software works in conjunction with
the Web server.
When used on the Web, PHP is an embedded scripting language. This means
that PHP code is embedded in HTML code. You use HTML tags to enclose the
PHP language that you embed in your HTML file. You create and edit Web
pages containing PHP the same way you create and edit regular HTML pages.
When PHP is installed, the Web server is configured to look for PHP code
embedded in files with specified extensions. It’s common to specify the
extensions .php or .phtml, but you can configure the Web server to look
for any extension. When the Web server gets a request for a file with the designated
extension, it sends the HTML statements as is, but PHP statements
are processed by the PHP software before they’re sent to the requester.
When PHP language statements are processed, the output consists of HTML
statements. The PHP language statements are not included in the HTML sent
to the browser, so the PHP code is secure and transparent to the user. For
example, consider this simple PHP statement:
<?php echo “<p>Hello World”; ?>
In this statement, <?php is the PHP opening tag, ?> is the closing tag, and
echo is a PHP instruction that tells PHP to output the text that follows it as
plain HTML code. The PHP software processes the PHP statement and outputs
the following:
<p>Hello World
This is a regular HTML statement that is delivered to the user’s browser. The
PHP statement itself is not delivered to the browser, so the user never sees
any PHP statements.
PHP and the Web server must work closely together. PHP is not integrated
with all Web servers but works with many of the most popular ones. PHP is
developed as a project under the Apache Software Foundation and, consequently,
works best with Apache. PHP also works with Microsoft IIS/PWS,
iPlanet (formerly Netscape Enterprise Server), and others.
15 Chapter 1: Getting to Know PHP
Keeping Up with Changes in PHP
PHP is open source software. If you have only used software from major software
publishers — such as Microsoft, Macromedia, or Adobe — you will find
that open source software is an entirely different species. It’s developed by a
group of programmers who write the code in their spare time, for fun and for
free. There’s no corporate office to call with questions. There’s no salesperson
to convince you of the wonders of the software. There’s no technical support
phone number where you can be put on hold.
Sounds like there’s no support for PHP, doesn’t it? Actually, quite the opposite
is true: An incredible amount of support is available. PHP is supported by the
developers and by the many PHP users. But you need to look for the support.
It’s part of your job as a PHP user and developer to search out the information
you need.
Open source software changes frequently, rather than once every year or two
as commercial software does. It changes when the developers feel it’s ready.
It also changes quickly in response to problems. When a serious problem,
such as a security hole, is found, a new version that fixes the problem may be
released in days. You don’t receive glossy brochures or see splashy magazine
ads for a year before a new version is released. If you don’t make the effort to
stay informed, you may miss the release of a new version or be unaware of a
serious problem with your current version.
16 Part I: Say Hello to the PHP Scripting Language
Serving up Web servers
The software that delivers Web pages to
the world is called a Web server. Several Web
servers are available, but the most popular one
is Apache. Approximately 60 percent of Web
sites on the World Wide Web use Apache,
according to surveys at www.netcraft.com
and www.securityspace.com/s_survey/
data/. Apache is open source software, which
means it’s free. It’s available for all major operating
systems. It’s automatically installed with
most Linux distributions and is preinstalled on
Mac OS X. You can find information about
Apache at httpd.apache.org. PHP is a project
of the Apache Software Foundation, so PHP
runs best with Apache.
Other Web servers are available. Internet Information
Server (IIS) is the second most popular
Web server with about 30 percent of the Web
sites. IIS is developed by Microsoft and runs
only on Windows. IIS is installed by default with
Windows server software. Other Web servers
include Zeus, NCSA, and Sun ONE. No other
Web server is used on more than 2.5 percent of
the Web sites.
Visit the PHP Web site often. You need to know the information that’s published
there. Join the mailing lists, which often are very high in traffic. When
you first start using PHP, the large number of mail messages on the discussion
lists brings valuable information into your e-mail box; you can pick up a lot by
reading those messages. And soon, you may be able to help others based on
your own experience. At the very least, subscribe to the announcement mailing
list, which only delivers e-mail occasionally. Any important problems or new
versions are announced here. The e-mail you receive from the announcement
list contains information you need to know.
So, right now, before you forget, hop over to the PHP Web site and sign up for
a list or two at www.php.net/mailing-lists.php.
PHP 5
Most of the important changes in PHP version 5 don’t affect the coding or the
use of PHP. They affect the performance of PHP. The Zend engine (the magic,
invisible engine that powers PHP) has been significantly improved, and as a
result, scripts run faster and more efficiently.
The object-oriented programming features of PHP are a major focus of PHP 5.
Object-oriented programming is greatly improved over PHP 4. The creation
and use of objects runs much faster, many object-oriented features have been
added, and exceptions are introduced. Programmers who prefer objectoriented
programming will be much happier with PHP 5. (Object-oriented
programming is described in Chapter 9.)
With PHP 5, the names of the PHP programs changed. PHP for the Web is
called php-cgi; PHP CLI is called just php, as in php.exe on Windows. Both
are stored in the directory where PHP is installed. Prior to PHP 5, both programs
were named php.exe, but stored in different subdirectories.
PHP 5 adds support for MySQL 4.1 and later. However, support for MySQL
is not included with PHP 5 by default. Support for MySQL 4.0 or MySQL 4.1
must be specified when PHP is installed. Prior to PHP 5, support for MySQL
4.0 and earlier was included automatically.
PHP 5 includes support for SQLite by default. SQLite provides quick and easy
methods for storing and retrieving data in flat files.
17 Chapter 1: Getting to Know PHP
Previous versions of PHP
You should be aware of some significant changes in previous PHP versions
because existing scripts that work fine on earlier versions may have problems
when they’re run on a later version, and vice versa. The following are some
changes you should be aware of:
Version 4.3.1: Fixed a security problem in 4.3.0. It’s not wise to continue
to run a Web site using versions 4.3.0 or earlier.
Version 4.3.0: Included significant improvements to the CLI version of
PHP, which is now built by default when you compile PHP from source
code (described in Appendix A). You must disable its build with installation
options if you don’t want it to be built.
Version 4.2.0: Changed the default setting for register_globals to Off.
Scripts running under previous versions may depend on register_
globals being set to On and may stop running with the new setting. It’s
best to change the coding of the script so that it runs with
register_globals set to Off.
Version 4.1.0: Introduced the superglobal arrays. Scripts written using
the superglobals (described in Chapter 6) won’t run in earlier versions.
Prior to 4.1.0, you must use the old style arrays, such as
$HTTP_POST_VARS.
By the time you read this, it’s possible that everyone has updated to PHP 5.
However, some IT departments and Web hosting companies may not update
immediately. Keep the previous changes in mind when using older versions.
18 Part I: Say Hello to the PHP Scripting Language
Chapter 2
Setting Up the Environment
In This Chapter
Getting access to PHP through Web hosting companies
Building your own Web site from scratch
Testing PHP
Now that you’ve decided to use PHP, your first task is to set up an environment
for PHP development. As I discuss in Chapter 1, PHP is used
most often to develop dynamic Web sites, so the majority of this chapter discusses
setting up PHP for use with a Web site. If you plan to use PHP only as a
general-purpose scripting language, independent of the Web, setting up your
environment is much simpler. You can skip the sections about setting up a
Web environment and go directly to the section, “Setting Up PHP for General-
Purpose Scripting.”
Establishing Your Web Environment
PHP for Web development runs in partnership with a Web server, as described
in Chapter 1. Thus, a Web site requires a Web server. To use PHP in your Web
site, the Web server must be able to exchange information with the PHP software,
and, thus, PHP must be installed where the Web server can access it.
The Web site environment involves more than just a Web server and PHP on
a computer. Here are a few other requirements:
The computer must be connected to the Internet.
The computer must have enough resources, such as disk space and
memory, to handle the expected Web traffic.
Other software, such as a database, may be required in the environment.
You may or may not be interested in setting up your own Web environment.
You may think that installing software is fun, or you may think it’s similar to
having the flu. If you want to install your own Web environment from scratch,
you can. You may even already have a Web site running on your own computer
and are just looking to add to its functionality by using PHP. If you don’t want
to install your own Web environment, you can use a Web environment installed
and maintained by someone else, such as the IT department at work or a
commercial Web hosting company. Perhaps you have an existing Web site at
a hosting company that you want to make more dynamic. You can use PHP in
either a Web environment of your own or one provided by someone else.
Another common development environment includes both your own Web
environment and one maintained by someone else. That is, it’s common for
developers to set up testing Web environments on their own computers where
they write and debug Web pages. Then, when everything is working correctly,
the Web pages are transferred to their Web site at work, maintained by the IT
department, or to a Web hosting company.
The following are some advantages of using someone else’s Web environment:
It’s easier than setting up your own: You just copy your Web pages onto
the other party’s computer, and that’s it. You don’t need to install any
software or hardware or resolve any computer problems. Someone else
handles that for you.
Less technical skill is required: You need to understand only Web languages,
such as HTML and PHP. You don’t need to know about Internet
connections, Web servers, computer administration, and other technical
things. Some people are very interested in these things, but some are not.
The advantages of running your own Web environment are as follows:
Control: You get to make all the decisions. You can set up the Web environment
the way that works best for you.
Access: You can access the computer whenever you want to work on
your Web site.
Stability: You know the Web site will be there as long as you need it. You
won’t wake up one morning to discover that your Web hosting company
has gone out of business and you have two days to move your site.
Security: Because you control the Web environment, you are the only
person who needs to access the computer. You can keep it under lock
and key. When you use a Web hosting company, other people have
access to the computer, and one of them may be a bad guy who’s after
your secrets.
20 Part I: Say Hello to the PHP Scripting Language
Using an existing Web environment
When you use a Web environment set up by someone else, you don’t need
to understand the installation and administration of the Web site software.
Someone else — your company’s IT department, a commercial Web hosting
company, your next-door neighbor — is responsible for the operation of the
Web site. It’s their job to provide you with a working Web site, including PHP
if it’s required. Your job is only to write and install the Web site files.
To use an existing Web environment, you need the following information from
the Web site administrator:
The location of Web pages: For the world to see your Web site, the files
containing the Web pages must be in a specific location on the computer.
The Web server that delivers the Web pages to the world expects to find
the files in a specific directory. You need to know where that directory is
and have access to the directory.
The Web page installation process: You need to know how to install the
files. In most cases, you send the files via FTP to the proper location. FTP
(File Transfer Protocol) is a method of copying a file from one computer
to another on a network. In some cases, you may copy the files directly
or use other methods to install the Web pages. You may need a user ID
and password to install the files.
The name of the default file: When users point their browsers at a URL, a
file is sent to them. The Web server is set up to send a specific default file
when the URL points to a directory. Very often the default file is named
index.htm or index.html, but sometimes other names are used, such as
default.htm. You need to know what you should name your default file.
The PHP file extension: When PHP is installed, the Web server is
instructed to expect PHP statements in files with specific extensions.
Frequently, the extensions used are .php or .phtml, but other extensions
can be used. PHP statements in files that do not have the correct extensions
won’t be processed. You need to know what extension to use for
your PHP scripts.
One of the disadvantages of hosting your site in an existing Web environment
is that you have no control over your development environment. The administrators
of the Web environment provide the environment that works best
for them. For instance, PHP has a myriad of options that can be set, unset, or
given various values. The administrators decide the option settings based on
their needs, which may or may not be ideal for your purposes. They probably
set up the environment for ease of maintenance, low cost, and minimal customer
defections. You can’t change certain parts of your environment; you
can only beg the administrators to change it. They will be reluctant to change
a working setup because a change may cause problems for their system or
for other customers.
21 Chapter 2: Setting Up the Environment
Choosing a Web hosting company
A Web hosting company provides everything you need to put up a Web site,
including the computer space and all the Web site software. You just create
the files for your Web pages and move them to a location specified by the
Web hosting company.
About a gazillion companies offer Web hosting services. Most charge a monthly
fee, which is often quite small, and some are even free. Most of the free ones
require you to display advertising. Usually, the monthly fee varies, depending
on the resources provided for your Web site. For instance, a Web site with
2MB (megabytes) of disk space for your Web page files costs less than a Web
site with 10MB of disk space.
When looking for a place to host your Web site, make sure that the Web hosting
company offers PHP. Some do not. Also, make sure the company offers a
recent version of PHP. Web hosting companies may not offer a version that
has just been released, but they should upgrade their PHP fairly soon after a
new version is released.
Don’t consider a Web hosting company that offers only PHP 3. PHP 4.3.1 was
released in February 2003, so no Web hosting company should still be providing
PHP older than 4.3.1, especially because a security issue was discovered
in earlier versions and was fixed in PHP 4.3.1. Ideally, by the time you read
this, most Web hosting companies will be offering PHP 5.
Other considerations when choosing a Web hosting company include the
following:
Reliability: You need a Web hosting company that you can depend on —
one that won’t go broke and disappear tomorrow. And you want one
that has enough computer power and other resources to keep your Web
site up. A Web site with more down time than up time is pretty useless.
Hopefully, some research on the Web or among colleagues will identify
Web hosting companies whose reliability is not up to snuff.
Speed: Web pages that download slowly are a problem because users
will get impatient and go elsewhere. Slow pages may be a result of a Web
hosting company that started its business on a shoestring and has a
shortage of good equipment, or the problem may be a Web hosting company
that is so successful that its equipment is overwhelmed by new
customers. Either way, Web hosting companies that deliver Web pages
too slowly are unacceptable. In some cases, you can find sites that are
hosted at the Web hosting company and see the download speed for
these sites. Sometimes the Web hosting company’s Web site provides
some customer links, or the company’s salespeople may provide you
with this information.
Technical support: Some Web hosting companies have no one available
to answer questions or troubleshoot problems. Technical support is
22 Part I: Say Hello to the PHP Scripting Language
often provided through e-mail only, which can be acceptable if the
response time is short. Sometimes you can test the quality of the company’s
support by calling the tech support number, or test the e-mail
response time by sending an e-mail.
Domain name: Each Web site has a domain name that Web browsers use
to find the site on the Web. Each domain name is registered, for a small
yearly fee, so that only one Web site can use it. Some Web hosting companies
allow you to use a domain name that you have registered independently
of the Web hosting company, some assist you in registering
and using a new domain name, and some require you to use their domain
name. For instance, suppose your company’s name is Good Stuff and you
want your Web site to be named JanetsGoodStuff. Some companies allow
your Web site to be JanetsGoodStuff.com, but some require that your
Web site be named JanetsGoodStuff.webhostingcompanyname.com,
or webhostingcompanyname.com/~GoodStuff, or something similar. In
general, your Web site will look more professional if you can use your
own domain name.
Features: You should select features based on the purpose of your Web
site. Usually a hosting company bundles its features into plans — more
features generally means higher cost. Some features to consider include
the following:
• Disk space: How many MB/GB (gigabytes) of disk space will your
Web site require? Media files, such as graphics or music files, can
be quite large.
• Data transfer: Some hosting companies charge you for sending
Web pages to users. If you expect to have a lot of traffic on your
Web site, this cost should be a consideration.
• E-mail addresses: Many hosting companies provide you with a
number of e-mail addresses for your Web site. For instance, if your
Web site is JanetsGoodStuff.com, you could allow users to send
you e-mail at me@JanetsGoodStuff.com.
• Software: Hosting companies offer access to a variety of software
for Web development. In addition to the PHP required for this
book, some hosting companies offer databases, such as MySQL or
PostgreSQL, and other development tools such as FrontPage extensions,
shopping cart software, credit card validation, and other tools.
• Statistics: Often hosting companies can help you gather statistics
regarding your Web traffic, such as the number of users, time of
access, access by Web page, and so on.
Backups: Backups are copies of your Web page files and your database
that are stored in case your files or database are lost or damaged. You
want to be sure that the company makes regular, frequent backup copies
of your application. You also want to know how long it would take for
backups to be put in place to restore your Web site to working order
after a problem.
23 Chapter 2: Setting Up the Environment
It’s difficult to research Web hosting companies from a standing start — a
search at Google for Web hosting results in over 4 million hits. The best way
to research Web hosting companies is to ask for recommendations from
people who have experience with those companies. People who have used a
hosting company can warn you that the service is slow or that the computers
are frequently down. After you have gathered a few names of Web hosting
companies from satisfied customers, you can narrow the list to the one that
is best suited and most cost-effective for your purposes.
24 Part I: Say Hello to the PHP Scripting Language
The domain name game
Every Web site needs a unique address on the
Web. The unique address used by computers to
locate a Web site is the IP address. It is a series
of four numbers between 0 and 255, separated
by dots — for example, 172.17.204.2 or
192.163.2.33.
Because IP addresses are made up of numbers
and dots, they’re not easy to remember.
Fortunately, most IP addresses have associated
names that are much easier to remember. Some
examples include amazon.com, www.irs.
gov, or mycompany.com. A name that is an
address for a Web site is called a domain name.
A domain can be one computer or many connected
computers. When a domain refers to several
computers, each computer in the domain
may have its own name. A name that includes
an individual computer name, such as thor.
mycompany.com, names a subdomain of
mycompany.com.
The domain or subdomain name is a required
component of the URL — the address that a
Web surfer types into the browser window to
identify the Web site he wants to visit. The URL
can contain more elements than just the domain
name, but often, the domain name (amazon.
com, for example) is all that is required. Or the
subdomain name (janet.valade.com, for
example) may be sufficient. When only the
domain name is used in the URL, the Web server
sends the file with the default filename, such
as index.htm or index.html. Or you can
include a filename in the URL, in addition to the
domain name, such as janet.valade.com/
links.html.
Each domain name must be unique to serve as
an address. Consequently, a system for registering
domain names ensures that no two locations
use the same domain name. Anyone can register
any domain name, as long as the name is not
already taken. You can register a domain name
on the Web. First, you test your potential domain
name to find out whether it is available. If it’s
available, you register it in your name or a company
name and pay the fee. The name is then
yours to use, and no one else can use it. The
standard fee for domain name registration is
$35.00 per year. You should never pay more, but
bargains are often available.
Many Web sites, including those of many Web
hosting companies, enable you to register a
domain name. A search at Google (google.
com) for “domain name register” results in over
2 million hits. Shop around to be sure you find
the lowest price. Also, many Web sites allow
you to enter a domain name and see who it is
registered to. These Web sites do a domain
name database search by using a tool called
whois. A search at Google for “domain name
whois” results in over half a million hits. A
couple places where you can do a whois
search are Allwhois (Allwhois.com) and
Better-Whois (betterwhois.com).
You can ask for names from colleagues and friends. Also, people often ask for
recommendations for hosting companies on the PHP discussion lists. Many
people on the lists have experience using PHP with Web hosting companies
and are glad to provide recommendations or warnings. Because people often
ask this question, you may get all the information you need from the list
archives, which you can search at marc.theaimsgroup.com/.
Setting up your own Web environment
If you’re starting a Web site from scratch, you need to understand the Web
site software fairly well. You have to make several decisions regarding hardware
and software. You also need to install a Web server and PHP, as well as
maintain, administer, and update the system yourself. Taking this route
requires more work and more knowledge. The advantage is that you have
total control over the Web development environment.
The following are the general steps for setting up the Web environment
needed for the activities described in this book:
1. Set up the computer.
2. Install the Web server.
3. Install PHP.
The first step is outside the scope of this book. You probably have a computer
but may be planning to install a new one for your Web site. For more
information on buying and setting up computers, pick up a copy of Buying a
Computer For Dummies or PCs For Dummies, 9th Edition, both by Dan Gookin
and published by Wiley Publishing, Inc. Web servers and PHP exist for almost
all hardware and operating systems, including many flavors of Unix and Linux,
Windows, and Mac OS X.
Installing the Web server
When your computer is set up and ready, you need to decide which Web server
to install. Apache is generally your best bet because it offers the following
advantages:
It’s free: What else do I need to say?
It runs on a wide variety of operating systems: Apache runs on
Windows, Linux, Mac OS, FreeBSD, and most varieties of Unix.
It’s popular: Approximately 60 percent of Web sites on the Internet use
Apache, according to surveys at www.netcraft.com/survey and at www.
securityspace.com/s_survey/data/. This wouldn’t be true if it didn’t
work well. Also, this means that a large group of users can provide help.
It’s reliable: After Apache is up and running, it should run as long as your
computer runs. Emergency problems with Apache are extremely rare.
25 Chapter 2: Setting Up the Environment
It’s customizable: The open source license allows programmers to modify
the Apache software, adding or modifying modules as needed to fit their
own environments.
It’s secure: Free software is available that runs with Apache to make it
into a secure SSL server. SSL is used to provide extra security for Web
sites that need to protect important information. It means that the information
passed between the Web server and the browser is encrypted so
that no one can intercept and read it. Security is an essential issue if
you’re using the site for e-commerce.
Apache is automatically installed when you install most Linux distributions.
Apache is also usually preinstalled on Mac. For most Unix flavors, you want
to download the Apache source and compile it yourself, although some
binaries (programs that are already compiled for specific operating systems)
are available. For Windows, you need to install a binary file, preferably on
Windows NT/2000/XP, although Apache also runs on Windows 98/Me.
As of this writing, Apache 1.3.27 is the current stable release. Apache 2 is also a
stable release, but it is still considered experimental to use PHP and Apache 2.
Check the PHP Web site (www.php.net) to find out the current status of PHP
and Apache 2 together. Apache information, software downloads, documentation,
and installation instructions for various operating systems are available
at the Apache Web site (httpd.apache.org). The Web site provides extensive
documentation.
Other Web servers are available. Microsoft offers Internet Information Server
(IIS), which is the second most-popular Web server on the Internet with
approximately 27 percent of Web sites. Sun offers iPlanet (formerly Netscape
Enterprise Server), which serves less than 5 percent of the Internet. Other
Web servers are available, but they have even smaller user bases.
Installing PHP
Many computer systems come with PHP already installed. Most Linux distributions
include PHP. Some newer versions of Mac OS X also come with PHP
installed. Before you install PHP, check whether it’s already installed by
searching your disk for any PHP files in the following manner:
Linux/Unix/Mac: At the command line, type the following:
find / -name “php*”
Windows: Use the Find feature (choose Start➪Find) to search for php*.
If you don’t find any PHP files, PHP is not installed. To install PHP, you need
access to the Web server for your site. For instance, when you install PHP
with Apache, you need to edit the Apache configuration file. All the information
and software you need is provided on the PHP Web site (www.php.net).
Detailed installation instructions are provided in Appendix A.
26 Part I: Say Hello to the PHP Scripting Language
If you do find PHP files, PHP is already installed, and you may not need to reinstall
it. Use the following considerations to decide whether to reinstall PHP:
Installation options: PHP may not have been installed with the options
you require. For instance, PHP may not have been installed with support
for the database that you’re planning to use. Support for ODBC is always
included, but support for MySQL, Oracle, MS SQL, and other databases
must be specified when PHP is installed. Support is also always included
for SQLite, XML, COM, FTP, and others, but other support is not automatically
included. If you’re planning to use another database or other
software or features, you may need to reinstall PHP with added support.
You can check which options were used when PHP was installed. Follow
the directions for testing PHP in the following section. If the test script
runs correctly, the table displayed by the phpinfo() statement shows
all the support that is included in your PHP installation. Check whether
the support you need is included. If it’s not, you need to reinstall. Detailed
instructions for installing PHP are provided in Appendix A.
Version: The installed version may not be the most recent. You need to
check the version of PHP that’s installed. You can check the version with
the following command:
php-cgi –v
For versions prior to PHP 5, the command to check the version is:
php –v
You may need to be in the same directory with the file php-cgi.exe (or
php.exe)to execute the preceding command. You see output similar to
the following that shows the version of PHP that is installed:
PHP 5.0.0 (cgi-fcgi), Copyright (c) 1997-2003 The PHP
Group
Zend Engine v2.0.0, Copyright (c) 1998-2003 Zend
Technologies
If the version is not the most recent, you should reinstall it. To see what
the latest stable version is, check www.php.net/downloads.php.
Testing PHP
After you have the information you need to use PHP on your Web site at the
Web hosting company or you have PHP installed on your own computer, you
need to test to make sure PHP is working correctly. To test whether PHP is
installed and working, follow these steps:
1. Locate the directory in which your PHP scripts need to be located.
27 Chapter 2: Setting Up the Environment
This directory and the subdirectories under it are called your Web space.
The default Web space for Apache is htdocs in the directory where
Apache is installed. For IIS, it is Inetpub\wwwroot. In Linux, it may be
/var/www/html. Different directories may be configured for your Web
space when the Web server is installed, so if someone other than you
installed the Web server, you may need to ask what the directory is. If
you’re using a Web hosting company, it will supply the directory name.
2. Create a file somewhere in your Web space with the name test.php
that contains the following code:
<html>
<head>
<title>PHP Test</title>
</head>
<body>
<p>This is an HTML line
<?php
echo “<p>This is a PHP line</p>”;
phpinfo();
?>
</body>
</html>
3. Point your browser at the file test.php created in Step 2 by typing
the URL to the file.
The URL will be in the format http://www.mycompany.com/test.php.
If your Web server, PHP, and the test.php file are on the same computer
you are testing from, you can type localhost/test.php.
In order for the file to be processed by PHP, you need to access the file
through the Web server, not by choosing File➪Open in your Web browser.
If your Web server, PHP, and test.php file are on the same machine you
are testing from, you can type localhost/test.php.
You should see the following in the Web browser:
This is an HTML line
This is a PHP line
Below these lines, you should see a large table, which shows all the information
associated with PHP on your system. It shows PHP information,
path names and filenames, variable values, what software is supported,
and the status of various options. For instance, if you scroll down
the table, you see a block of options for FTP that says: FTP support
enabled.
The table is produced by the line phpinfo() in the test script. Any time
you have a question about the settings for PHP, you can use the statement
phpinfo() to display this table and check settings. The phpinfo()
statement is used often throughout this book.
28 Part I: Say Hello to the PHP Scripting Language
If there are problems with the PHP installation, you might get one of the following
results from the test file:
You see only This is an HTML line. The PHP lines and the table of
information are not displayed.
You see a blank page.
The browser displays a download window rather than the Web page.
If you get a problem result from the test file and you are not the system
administrator, you need to talk to the person who installs and maintains the
software, such as an IT staff member at work or a technical support person at
your Web hosting company. It’s their responsibility to diagnose your problem.
If you get a problem result from the test file and you installed the software
yourself, first check to see that PHP is installed. At the command line, change
to the directory where PHP is installed and type the following:
php-cgi –v
or
php -v
If PHP returns information about its version, PHP is installed. Be sure that
you accessed the test file as instructed in Step 3 in the preceding list. Notice
the warning for that step.
Be sure that the file test is in a directory in your Web space, as described in
Step 1 of the preceding steps. In Apache, you can check the httpd.conf file
for a line similar to the following line:
DocumentRoot “C:/Program Files/Apache Group/Apache/htdocs”
This line tells Apache where to look for Web page files.
Double-check the script to make sure you typed it correctly. The script is also
available for download from my Web site: janet.valade.com.
If you are accessing the test file correctly and it seems to be entered correctly,
the problem is probably in your configuration. Reread the instructions for
configuring PHP at the end of Appendix A and make sure that you followed all
the instructions. In particular, check the following:
The Web server is configured to know which file extensions to check for
PHP code. In Apache, check that the following line is included in the
httpd.conf file:
AddType application/x-httpd-php .php
29 Chapter 2: Setting Up the Environment
This line tells Apache to look for PHP code in files with the extension
.php. For IIS, access the console, as described in Appendix A, and check
the extension tab to be sure the correct extension is set.
Check to be sure the other lines were correctly added to the httpd file
for Apache, as described in the configuration sections for the appropriate
operating system in Appendix A. Check for any possible misspellings.
Also check that the lines were added in the correct location.
If you’re using IIS, check for the following line in php.ini:
cgi.force_redirect = 0
If your php.ini doesn’t contain this line, add it. If you have the line with
a semicolon at its beginning, remove the semicolon. If you find a line
with a setting of 1 rather than 0 (zero), change it to 0.
If you check everything carefully and are still having problems, it’s possible
that you have something unusual in your computer setup or your Web server
that is causing the problem. Read all the online documentation related to
installation at the PHP Web site. Search the Web site for information on installation
problems. You can find a wealth of information there.
If you still can’t find the answer, take your question to the PHP discussion
lists. First, search the archives at marc.theaimsgroup.com/. It’s possible
that someone has previously asked the same question and you can find the
answer quickly in the archives. If not, post your question to the discussion
list. Include the following information in your question:
Indicate the name and version of the operating system you’re using.
Identify the PHP version you’re trying to install.
Copy the content of the test file into your message.
Describe the exact output that you see in your Web page.
People on the list are very knowledgeable and will help you solve your
problem.
Setting Up PHP for General-
Purpose Scripting
PHP runs by itself when used as a general-purpose programming language.
You don’t need to have a Web server installed if you’re not using PHP with a
Web site. The command line version of PHP — PHP CLI — is a separate program,
different than the PHP program you use for Web sites. It needs to be
installed separately.
30 Part I: Say Hello to the PHP Scripting Language
Even if your machine came with PHP installed, PHP CLI may not be there. You
can check to see if PHP is on your computer and which version is there. By
default, you should find the file in the directory where PHP is installed. The
PHP CLI file is named php.exe and the PHP CGI file is named php-cgi.exe.
(Prior to PHP 5, the files were both named php.exe, but stored in different
subdirectories. PHP CLI was stored in a subdirectory named /cli.)Or PHP
CLI may have been installed in another location. You can search your disk for
all PHP files as follows:
Linux/Unix/Mac: Type the following at the command line:
find / -name “php*”
Windows: Use the Find feature (choose Start➪Find) to search for php*.
If you find any PHP files that you think might be PHP CLI, you can check
by changing to the directory where the PHP program file is and typing the
following:
php –v
The output will include either cgi or cli, similar to the following:
PHP 5.0.0 (cli) (built: Jun 15, 2003 23:07:34)
Notice that the output includes (cli). If it’s not the CLI version, it shows
(cgi). The previous command also serves to test whether PHP CLI is working.
If it responds with the version number rather than an error message, it’s
working.
If you don’t find PHP CLI, you need to install it before you can use PHP for
tasks that are unrelated to the Web. Appendix A provides detailed PHP installation
instructions, including instructions for PHP CLI.
If you’re going to use PHP for both Web sites and general-purpose programming,
you need to install two different PHP programs, the version for the Web
and PHP CLI. Both need to be the same version of PHP. That is, if you install
PHP 5.0.0 for the Web, be sure that you’re using PHP CLI 5.0.0 as well. In
Windows, PHP requires a file called php5ts.dll, which is in your main PHP
directory. You need to use the same version of PHP so that both PHP programs
use the same version of php5ts.dll. (See Appendix A for details.)
31 Chapter 2: Setting Up the Environment
Configuring PHP
PHP is very flexible. Configuration settings determine some of PHP’s behavior,
such as whether it displays error messages, A file called php.ini stores the
configuration settings. You can change the setting by editing php.ini.
When PHP is installed, php.ini is created, as described in Appendix A. If
you install PHP yourself, remember where you put php.ini. You may need
to change it. If you’re using PHP, but someone else is the PHP administrator
(for instance, if you’re using a Web hosting company), you are unlikely to
have access to php.ini. If you need to make a change to the PHP settings,
you will have to ask the administrator. For some settings, you can add statements
to your script to change the settings temporarily, for that script only.
Specific statements that change settings temporarily are discussed in context
throughout this book.
Using Tools to Build PHP Scripts
PHP scripts are just text files. You can use your favorite tool for writing text
files to write PHP scripts. Many scripts have been written with vi, Notepad, or
WordPad. However, you can find tools that make script writing much easier.
It’s worthwhile to check out programming editors and Integrated Development
Environments (IDEs) before creating your PHP scripts. These tools offer features
that can save you enormous amounts of time during development. So
download some demos, try out the software, and select the one that suits
you best. You can take a vacation on the time you save later.
Programming editors
Programming editors offer many features specifically for writing programs.
The following features are offered by most programming editors:
Color highlighting: Highlight parts of the script — such as HTML tags,
text strings, keywords, and comments — in different colors so they’re
easy to identify.
Indentation: Automatically indent inside parentheses and curly braces
to make scripts easier to read.
Line numbers: Add temporary line numbers. This is important because
PHP error messages specify the line where the error was encountered. It
would be cumbersome to have to count 872 lines from the top of the file
to the line that PHP says is a problem.
32 Part I: Say Hello to the PHP Scripting Language
Multiple files: Can have more than one file open at once.
Easy code inserting: Buttons for inserting code, such as HTML tags or
PHP statements or functions.
Code library: Save snippets of your own code that can be inserted by
clicking a button.
Many programming editors are available on the Internet for free or for a low
price. Some of the more popular editors include the following:
Arachnophilia: (www.arachnoid.com/arachnophilia/) This multiplatform
editor is written in Java. It’s CareWare, which means it doesn’t
cost any money.
BBEdit: (www.barebones.com/products/bbedit/index.shtml) This
editor is designed for use on a Mac. BBEdit sells for $179.00. Development
and support have been discontinued for BBEdit Lite, which is free, but it
can still be found and legally used. TextWrangler is offered for $49 as a
replacement for BBEdit Lite.
EditPlus: (www.editplus.com) This editor is designed for use on a
Windows machine. EditPlus is shareware, and the license is $30.
Emacs: (www.gnu.org/software/emacs/emacs.html) Emacs works
with Windows, Linux, and Unix, and it’s free.
HomeSite: (www.macromedia.com/software/homesite/) HomeSite is
designed for use with Windows and will run you $99.00.
HTML-Kit: (www.chami.com/html-kit/) This is another Windows
editor that you can pick up for free.
vim and gvim: (www.vim.org/) These free, enhanced versions of vi can
be used with Windows, Linux, Unix, and Mac OS. The gvim editor has a
GUI that makes Windows users feel more at home.
Integrated Development
Environment (IDE)
An Integrated Development Environment (IDE) is an entire workspace for
developing applications. It includes a programming editor as well as other
features. Some features included by most IDEs are the following:
Debugging: Has built-in debugging features.
Previewing: Displays the Web page output by the script.
Testing: Has built-in testing features for your scripts.
33 Chapter 2: Setting Up the Environment
FTP: Has built-in ability to connect and upload/download via FTP. Keeps
track of which files belong in which Web site and keeps the Web site upto-
date.
Project management: Organizes scripts into projects; manages the files
in the project; includes file checkout and check-in features.
Backups: Makes automatic backups of your Web site at periodic intervals.
IDEs are more difficult to learn than programming editors. Some are fairly
expensive, but their wealth of features can be worth it. IDEs are particularly
useful when several people will be writing scripts for the same application.
An IDE can make project coordination much simpler and make the code more
compatible.
The following are popular IDEs:
Dreamweaver MX: (www.macromedia.com/dreamweaver) This IDE is
available for the Windows and Mac platforms. It provides visual layout
tools so you can create a Web page by dragging elements around and
clicking buttons to insert elements. Dreamweaver can write the HTML
code for you. It includes the HomeSite editor so you can write your own
code. It also supports PHP. Dreamweaver will set you back $399.00.
Komodo: (www.activestate.com/Products/Komodo/) Komodo is
offered for the Linux and Windows platforms. It’s an IDE for open source
languages, including Perl and Python, as well as PHP. It’s offered for
$29.95 for personal or educational use, and $295.00 for commercial use.
Maguma: (www.maguma.com) Maguma is available for Windows only. It’s
an IDE for Apache, PHP, and MySQL on Windows and comes in two versions
at different costs: Maguma Studio Desktop and Maguma Studio
Enterprise, which offers features for huge sites with multiple servers.
Maguma Studio for PHP is a free version with support for PHP only.
PHPEdit: (www.phpedit.net/products/PHPEdit/) This free IDE is
available only for Windows.
Zend Studio: (www.zend.com/store/products/zend-studio.php)
Zend Studio is offered for the Linux and Windows platforms. This IDE
was developed by the people who developed the Zend engine, which is
the engine under the hood of PHP. These people know PHP extremely
well. Zend Studio will run you $195.00.
A Web page describing editors and IDEs useful with PHP is available at
phpeditors.linuxbackup.co.uk. Currently 111 editors are listed.
34 Part I: Say Hello to the PHP Scripting Language
Chapter 3
Creating Your First PHP Script
In This Chapter
Writing PHP statements
Adding PHP sections to HTML files
Writing PHP output statements
Documenting your scripts
APHP statement is an instruction that tells PHP to perform an action. A
PHP script is a series of PHP statements. Theoretically, a script can contain
as few as one statement, but it’s unlikely that any practical script would
consist of a single statement. In most cases, you write scripts that contain
several statements in a row. PHP executes the statements one at a time until
it reaches the end of the script.
As discussed in Chapter 1, PHP can do many things, and scripts are the
method you use to tell PHP what you want it to do. You can tell it to display
some text on a Web page or to store data that a user entered into a form on
your Web page. PHP can also do things that are unrelated to Web sites, such
as back up all the files in a directory on your hard disk. You can write simple
scripts that just display hello in a Web browser. Or you can write complicated
scripts that display different things in the Web browser for different people,
or request passwords from Web site visitors and refuse access to visitors who
don’t enter valid passwords. Applications often consist of two or more scripts
that work together to accomplish the job required. A large, complicated application,
such as an e-commerce application, can consist of many scripts.
In this chapter, I explain how to write your first script. I also discuss output
statements, which are the most common PHP statements. Finally, I illustrate
the importance of documenting your script.
Writing PHP Statements
A PHP statement tells PHP to perform an action. One of the most common
PHP statements is the echo statement. Its purpose is to display output. For
instance, take a look at the following echo statement:
echo “Hi”;
An echo statement says to output everything that is between the double
quotes (“). So, this statement tells PHP to output the word Hi.
The echo statement is a simple statement. PHP simple statements end with a
semicolon (;). PHP reads a simple statement until it encounters a semicolon
(or the PHP closing tag, discussed later in this chapter). PHP ignores white
space. It doesn’t care how many lines it reads. It doesn’t consider the content
or the syntax of the statement. It just reads until it finds a semicolon and then
interprets the entire content as a single statement.
Leaving out the semicolon is a common error, resulting in an error message
that looks something like this:
Parse error: expecting `’,’’ or `’;’’ in file.php on line 6
Notice that the error message gives you the line number where it encountered
problems. Usually, the error is that the semicolon was left off in the line before
the indicated line. In this case, the semicolon is probably missing on line 5.
You may prefer to use an editor that displays line numbers. Debugging your
PHP scripts is much easier this way. Otherwise, you need to count the lines
from the top of the script to find the line containing the error. If your script
contains six lines, counting them is no big deal. If your script contains 553
lines, however, this is less than fun. Some editors allow you to indicate a line
number, and the editor takes you directly there.
As far as PHP is concerned, an entire script full of simple statements can be
written in one long line, as long as the statements are separated by semicolons.
However, a human would have a tough time reading such a script. Therefore,
you should put simple statements on separate lines.
Sometimes several statements are combined into a block, which is enclosed
by curly braces ({}). Statements in a block execute together. A common use
of a block is in a conditional statement where statements are executed only if
certain conditions are met. For instance, you may want to include the following
instructions:
36 Part I: Say Hello to the PHP Scripting Language
if (time = midnight)
{
put on pajamas;
brush teeth;
go to bed;
}
The statements are enclosed in curly braces to ensure they execute as a block.
If it’s midnight, then all three actions within the block are performed. If the
time is not midnight, none of the statements execute (no pajamas, no clean
teeth; no going to bed).
PHP statements that use blocks, such as if statements, are called complex
statements. PHP reads the entire complex statement, not stopping at the first
semicolon it encounters. PHP knows to expect one or more blocks and looks
for the ending curly brace of the last block in complex statements. Notice that
there is a semicolon before the ending brace. This semicolon is required, but
no semicolon is required after the ending curly brace.
Notice that the statements inside the block are indented. Indenting is not
necessary for PHP. Indenting is strictly for readability. You should indent the
statements in a block so that people reading the script can tell more easily
where a block begins and ends. One of the more common mistakes when
writing scripts is to leave out a closing curly brace, particularly when writing
blocks inside blocks inside blocks. Tracking down a missing brace is much
easier when the blocks are indented.
Building Scripts
To build a script, you add PHP statements one after another to a file that you
name with a .php extension. Actually, if you are wise, you write the script
on paper first, unless the script is very simple or you are quite experienced.
Planning makes programming much less prone to errors.
If you’re writing a PHP script for your Web site, you insert the PHP statements
into the file that contains the HTML for your Web page. If you’re writing a script
that will run independent of the Web, you type the PHP statements into a file
and then you run the script by calling PHP directly. The following sections
describe how to do this.
37 Chapter 3: Creating Your First PHP Script
Adding PHP statements to HTML pages
If you’re using PHP for your Web site, you do so by adding PHP code to your
HTML Web pages. HTML files that have PHP code in them should be named
with a .php extension so that the Web server knows to check the file for PHP
code. (Actually, the Web server administrator may have specified other
extensions, such as .php4 or .phtml, to indicate files that can contain PHP
code, but .php is the most common extension. In this book, I assume that the
appropriate extension is .php.)
You add PHP code to your Web page by using tags, similar, but not identical,
to other tags in the HTML file. The PHP code section is enclosed in PHP tags
with the following form:
<?php
. . .
PHP statements
. . .
?>
38 Part I: Say Hello to the PHP Scripting Language
How the server processes PHP files
When a browser is pointed to a regular HTML file
(a file with an .html or .htm extension), the
Web server sends the file, as is, to the browser.
The browser processes the file and displays the
Web page that is described by the HTML tags in
the file. When a browser is pointed to a PHP file
(a file with a .php extension), the Web server
looks for PHP sections in the file and processes
them, rather than just sending them as is to
the browser. The steps the Web server uses to
process a PHP file are as follows:
1. The Web server starts scanning the file in
HTML mode.
It assumes that the statements are HTML
and sends them to the browser without any
processing.
2. The Web server continues in HTML mode
until it encounters a PHP opening tag
(<?php).
3. When the Web server encounters a PHP
opening tag, it switches into PHP mode.
This is sometimes called escaping from
HTML. The Web server assumes all subsequent
statements are PHP statements and
executes the PHP statements. If there is
output, the server sends the output to the
browser.
4. The Web server continues in PHP mode
until it encounters a PHP closing tag (?>).
5. When the Web server encounters a PHP
closing tag, it returns to HTML mode.
The scanning is then resumed, and the
cycle continues from Step 1.
Sometimes you can use a shorter version of the PHP tags. You can try using
<? and ?>, without including the php. If short tags are enabled, you can save
a little typing. You enable or disable short tags in the php.ini file.
Using short tags is sometimes not a good idea. If you move your site to a
server where short tags are not enabled, all your PHP tags will quit working.
So if you think you might ever move your Web site, using the regular tags is
safer.
All statements between the two PHP tags are passed to PHP by the Web server
and are processed by the PHP preprocessor. After processing, the PHP section
is discarded. If the PHP statements produce output, the output is sent back
to the Web server, which then sends the HTML and the output from the PHP
sections to the browser. The browser does not see the PHP section, only its
output (if there is any output).
For example, you can add the following PHP section to your HTML file. Don’t
forget to give the HTML file a .php extension:
<?php
echo “This line brought to you by PHP”;
?>
When the Web server gets the file and sees the .php extension, it checks for
PHP tags. When it finds the PHP tag, it executes the PHP echo statement
instead of sending it to the browser. Only the output from the PHP section,
which is This line brought to you by PHP, is sent on to the browser. In
your browser window, you see the output at the location in the page where
you added the PHP section. Even if you view the source in your browser, you
only see the output, not the PHP code.
Don’t look at the PHP file directly with your browser. That is, don’t choose
File➪Open➪Browse in your browser to navigate to the file and click it. You
must point at the file using its URL, as discussed in Chapter 2. If you see the
PHP code (and not the output) displayed in the browser window, you may
not have pointed to the file by using its URL.
You can add several PHP sections to a Web page. For instance, you could
have the following code in your file:
HTML statements
<?php
echo “This line brought to you by PHP”;
?>
HTML statements
<?php
echo “This line also brought to you by PHP”;
?>
39 Chapter 3: Creating Your First PHP Script
Both lines echoed by PHP appear in your Web page at the locations where
you inserted the PHP sections.
Using PHP independent of the Web
To use PHP as a general scripting language, independent of the Web, you use
the version of PHP called CLI, which stands for Command Line Interface. PHP
CLI is a different version of PHP than the version used with a Web server
(usually called PHP CGI). PHP CLI is created separately when PHP is installed.
Instructions for installing the CLI version are provided in Appendix A.
If you want to use the CLI version, you’re probably running PHP on Linux or
Unix. Windows programmers are much less likely to need to write generalpurpose
PHP scripts, but they can if they need to. In this section, I provide the
information for the Linux/Unix version, but most of the information is also
true when working on Windows. (In some places, I point out the differences.)
The following is a PHP script:
<?php
echo “This line brought to you by PHP”;
?>
40 Part I: Say Hello to the PHP Scripting Language
Running PHP scripts on Linux/Unix
If you’re used to running shell scripts or Perl
scripts on Linux/Unix, you can run PHP scripts
in the same way. You can add a line to the top of
your script that directs the script to run with
PHP CLI, as follows, so that you can just run the
script directly without manually calling PHP:
#! /usr/bin/php
<?php
echo “This line brought to
you by PHP”;
?>
The first line tells the script to execute by using
the program found at /usr/bin/php. This line
does not work for Windows, but it doesn’t do
any damage when run on Windows. You can
include the first line when you write the script
so that it is more convenient on Unix/Linux and
not worry about having a broken script if you
move the script to Windows.
You execute the program by typing its name. You
may need to be in the same directory where the
program is located, unless it is in a directory on
your system path, or you can type the entire
path name to the PHP script. For instance, if the
preceding script is called test.php, you can
execute it by typing the following:
test.php
Or you may need to type the entire path:
/mystuff/test.php
You need to give the file execute permission, as
you do for any other script that you want to execute
directly.
If you have a file named testcli.php containing this PHP code, you can run
it from the command line by having the file in the same directory where PHP
is installed and by typing the following:
php testcli.php
Or you can type the entire path name to PHP, as in the following example:
/usr/local/php/cli/php testcli.php
For Windows, use the command prompt. You enter command prompt mode
by choosing the appropriate entry on your menu. Usually, you choose Start➪
Programs➪Accessories➪Command Prompt.
The CLI version of PHP differs from the CGI version in the following ways:
Outputting HTTP headers: Because the CGI version sends its output to
the Web server and then to the browser, it outputs the HTTP headers
(statements the Web server and browser use to communicate with each
other). Thus, the following is the output when the CGI version runs the
script in the previous example:
Content-type: text/html
X-Powered-By: PHP/5.0
This line brought to you by PHP
You don’t see the two headers on your Web page, but PHP for the Web
sends these headers because the Web server needs them. The CLI version,
on the other hand, does not automatically send the HTTP headers
because it is not sending its output to a Web server. The CLI output is
limited to the following:
This line brought to you by PHP
Formatting error messages: The CGI version formats error messages
with HTML tags, because the errors are expected to be received by a
browser. The CLI version does not use HTML formatting for error messages;
it outputs error messages in plain text.
Providing argc and argv by default: The argc and argv variables allow
you to supply data to the script from the command line (similar to argc
and argv in C and other languages). You aren’t likely to want to pass
data to the CGI version, but you are likely to want to pass data to the CLI
version. Therefore, argv and argc are available by default in the CLI version
and not in the CGI version. (The argv and argc built-in variables
are explained in Chapter 5.)
41 Chapter 3: Creating Your First PHP Script
When you run PHP CLI from the command line, you can use several options
that affect the way PHP behaves. For instance, -v is an option that displays
the version of PHP being accessed. To use this option, you would type the
following:
php –v
Table 3-1 shows the most useful PHP command-line options.
Table 3-1 PHP Command-Line Options
Option What It Does
-c Defines the path to the php.ini file to be used. This can be a different
php.ini file than the one used by the CGI version. For example,
-c /usr/local/php/cli/php.ini. (See Appendix A for more
on php.ini.)
-f Identifies the script to be run. For example, php -f /myfiles/
testcgi.php.
-h Displays a help file.
-i Displays PHP information in text output. Gives the same information as
phpinfo() (described in Chapter 2).
-l Checks the script file for errors, but doesn’t actually execute the code.
-m Lists the modules that are compiled into PHP. (See Chapter 14 for more
on modules.)
-r Runs PHP code entered at the command line. For example, php -r
‘print(‘Hi’);’.
-v Displays the version number of PHP.
Writing Your First Script
It’s sort of a tradition that the first program you write in any language is the
Hello World program. You may have written a Hello World program in
HTML when you first learned it. If you did, it probably looked similar to the
following HTML file:
42 Part I: Say Hello to the PHP Scripting Language
<html>
<head><title>Hello World HTML Program</title></head>
<body>
<p>Hello World!</p>
</body>
</html>
If you point your browser at this HTML program, you see a Web page that displays
the following output in the browser window:
Hello World!
Your first PHP script is a script that does exactly the same thing. The following
code is a PHP script that includes both HTML and PHP code and displays
Hello World! in a browser window:
<html>
<head><title>Hello World Script</title></head>
<body>
<?php
echo “<p>Hello World!</p>”
?>
</body>
</html>
If you point your browser at this script, it displays the same Web page as the
HTML script.
Don’t look at the file directly with your browser. That is, don’t choose File➪
Open➪Browse from your browser menu to navigate to the file and click it.
You must point at the file by typing its URL, as discussed in Chapter 2. If you
see the PHP code displayed in the browser window, instead of the output you
expect, you may not have pointed to the file by using its URL.
In this PHP script, the PHP section consists of the following code:
<?php
echo _<p>Hello World!</p>_
?>
The PHP tags enclose only one statement — an echo statement — that simply
outputs the text between the double quotes.
When the PHP section is processed, it is replaced with the output. In this
case, the output is as follows:
<p>Hello World!</p>
43 Chapter 3: Creating Your First PHP Script
If you replace the PHP section in the HTML version of Hello World with the
preceding output, the script now looks exactly like the HTML program. If you
point your browser at either program, you see the same Web page. If you look
at the source code that the browser sees (in the browser, choose View➪
Source), you see the same source code listing for both programs.
Discovering More about
Output Statements
In your Hello World script, created in the preceding section, you used an
echo statement, which is a good example of an output statement. Output
statements are used in almost every PHP script. It’s rare that you would write
a script that would do something and not output anything. True, a script can
do things that are invisible, like checking your entire hard disk to see if a certain
file exists. You would not see it checking. However, the search is pretty
pointless if the script doesn’t tell you what it found. You’d want to know where
it looked, when it finished, and whether or not it found the file. Because of
this, almost all scripts use output statements.
The general format of the echo statement is as follows:
echo outputitem1,outputitem2,outputitem3, . . .
Keep the following points in mind when working with echo statements:
An outputitem is a number or a string of characters. Numbers are things
like 1 or 250. A string is a string of characters, which can include numbers.
See Chapter 5 for a discussion of data types.
Enclose a string of characters with single or double quotes. (Chapter 5
explains when to use which type of quotes.)
List as many outputitems as you need.
Separate each outputitem with a comma. No space is added between
outputitems.
If you want a space in your output, add it as a character in a character
string.
44 Part I: Say Hello to the PHP Scripting Language
Table 3-2 shows some echo statements and their output.
Table 3-2 echo Statements
Echo Statement Output
echo 123; 123
echo “Hello World!”; Hello World!
echo “Hello”,”World!”; HelloWorld!
echo “Hello”,” “,”World!”; Hello World!
echo Hello World!; Not valid because the string is not enclosed
in quotes; results in an error message
echo ‘Hello World!’; Hello World!
Processing PHP output statements
The Hello World script, like most PHP scripts for the Web, is written mainly
to output HTML code that the browser then processes and displays in your
Web page. When writing PHP code to deliver output to a Web browser, you
need to keep in mind that there are two stages, as follows:
1. PHP processes the PHP statement and sends the output to the Web
server, which sends the output to the browser.
PHP does not know anything about HTML code and just sends the output
according to the instructions you write in the PHP output statement.
2. The Web browser receives the output from PHP, interprets it as HTML
statements, and displays a Web page accordingly.
The Web browser only understands HTML, not PHP code, so make sure
your PHP output is understandable to your browser.
Consider the echo statement from the Hello World script:
echo _<p>Hello World!</p>_
45 Chapter 3: Creating Your First PHP Script
The echo statement says to output everything that is between the double
quotes (“). So, for this statement, the two stages are as follows:
1. When PHP processes the echo statement, it outputs the following:
<p>Hello World!</p>
PHP does not understand HTML, so it does not know that <p> is an HTML
tag and does not see <p> as any sort of instruction. It just outputs the
statement as text.
2. The Web browser receives the output, recognizes that <p> is an HTML
tag, and displays the output on the Web page according to the HTML
tags. You see the following on the Web page:
Hello World!
The HTML tags <p> and </p> indicate the beginning and end of a paragraph
and are interpreted by the Web browser, but not displayed on the
screen. To see what PHP sent to the browser, view the source by using
the selections on your Web browser menu. For instance, in Internet
Explorer 5.5, choose View➪Source. For this Web page, the source would
show the following:
<p>Hello World!</p>
Using special characters
in output statements
The echo statement interprets some special characters that affect the output.
One common special-character combination is \n, which starts a new line in
the output of an echo statement. For example, write the following line:
echo _<p>Hello\n World!</p>_
The \n tells PHP that the output should start a new line. However, this does
not result in a new line on the Web page. To get a new line in the Web page,
you need to send the HTML code for a new line, which is <br>. Therefore, to
see the output on two lines in the Web page, you use the following statement:
echo _<p>Hello<br> World!</p>_
46 Part I: Say Hello to the PHP Scripting Language
A comparison of echo statements in Table 3-3 shows the differences in output
at Stage 1 (the PHP output stage) and Stage 2 (the Web browser display stage).
The first column contains the echo statement used in a PHP script. The second
column shows the output sent by PHP to the browser. The third column is
the output displayed on the Web page after the PHP output is interpreted
by the browser as HTML code.
Table 3-3 Stages of Web Page Delivery
Echo Statement PHP Output Web Page Display
echo “Hello World!”; Hello World! Hello World!
echo “Hello”; HelloWorld! HelloWorld!
echo “World!”;
echo “Hello\nWorld!”; Hello Hello World!
World!
echo “Hello<br>World!”; Hello<br>World Hello
World!
echo “Hello <br>\nWorld!”; Hello <br> Hello
World! World!
Notice where spaces are included in the output. The first echo statement
includes a space so the space is output. The second row has two echo statements,
but neither includes a space, so no space appears in the Web page. The
third row shows a space on the Web page, even though no space is included
in the echo statement. The space is added by the browser when it reads the
PHP output as HTML. In HTML, a new line is not displayed as a new line; it is
just interpreted as a single space.
Use \n liberally. Otherwise, your HTML source code will have some really
long lines. For instance, if you echo a long form, the whole thing may be
one long line in the source code, even though it looks fine in the Web page
because you used <br> in all the right places. If your Web page doesn’t display
correctly, you may need to troubleshoot the problem in the Web page
source code, a difficult process if your source code is one mile-long line. Use
\n to break the HTML source code into reasonable lines. Taking the extra
time to add these line breaks will pay off if you have to troubleshoot a Web
page. In addition, some browsers don’t handle mile-long lines very well.
47 Chapter 3: Creating Your First PHP Script
PHP executes output statements as instructed. PHP doesn’t care whether the
output is going to the Web or displayed on the screen. It’s your job to know
what kind of output you need. If you’re writing PHP scripts for use on the Web,
the output needs to be in HTML statements. If you’re writing code for independent
scripts, executed outside the Web environment, the output needs to be
in plain text format for display on the screen.
Documenting the Script
Adding comments to your script is essential. Comments describe your
script — what it does and how it does it. The larger, more complicated, or
more unusual your code is, the more you need comments. After working
20 hours a day on a script, you may believe its code is permanently burned
into your brain. From experience, however, I know that two years from now,
when you need to revise this script, you will swear it was written by a stranger.
And there’s also the possibility that your scripts may need to be revised by
an actual stranger. You may be long gone, retired in luxury in the Bahamas,
when your scripts need to be revised.
Comments are notes that are embedded in the script itself. PHP ignores comments;
comments are for humans. You can embed comments in your script
anywhere as long as you tell PHP that they are comments. The format for
comments is as follows:
/* comment text
more comment text */
Your comments can be as long or as short as you need. When PHP sees code
that indicates the start of a comment (/*), it ignores everything until it sees
the code that indicates the end of a comment (*/).
It is customary and useful to put a block of comments at the top of your script
giving information about the script and an overview of what it does. For example,
here’s one possible format for a comment block at the top of your script:
/* name: hello.php
description: Displays “Hello World!” on a Web page.
written by: Joe Programmer
created: 2/1/03
modified: 3/15/03
*/
48 Part I: Say Hello to the PHP Scripting Language
PHP also has a short comment format. You can specify that a single line is a
comment by using the # or two slashes (//) in the following manner:
# This is comment line 1
// This is comment line 2
You can also use # or // in the middle of a line to signal the beginning of a
comment. PHP will ignore everything from the # or // to the end of the line.
This is useful for commenting a particular statement, as follows:
echo “Hello”; // this is my first output statement
PHP comments are not included in the HTML code that is sent to the user’s
browser, so the user does not see these comments.
It’s helpful to use descriptive comments as titles for sections of code, such as
the following:
/* Check whether the customer is over 18 years old */
/* Store the information in the database */
/* Search for the selected file name */
Sometimes you really want to emphasize a comment. The following format
makes a comment very noticeable:
######################################
## Double-Check This Section ##
######################################
Use comments as often as necessary in the script to make it clear. However,
using too many comments is a mistake. Don’t comment every line or everything
you do in the script. If your script is too full of comments, the really
important comments can get lost in the maze. Only use comments to label
sections and to explain code that is unusual or complicated, not code that is
obvious. For instance, the previous comment, documenting the echo statement,
is not a useful comment in most cases. It’s obvious what the code is
doing; a comment isn’t needed.
Be careful that you don’t get your comments mixed together. For instance, if
you nest one comment section inside another, PHP can’t handle it. For
instance, a comment such as the following won’t work:
/* This is the first comment.
/* This is the comment nested inside */
*/
49 Chapter 3: Creating Your First PHP Script
PHP looks at the opening /* of the first comment and ignores everything until
it comes to the first */. It ignores the second /* because it considers it part of
a comment. PHP considers the comment ended after the first */ and outputs
an error message when it comes to the second */. PHP doesn’t recognize the
second */ as closing a comment because it isn’t in comment mode.
50 Part I: Say Hello to the PHP Scripting Language
Part II
Variables and Data
In this part . . .
In this part, I describe the use of variables in PHP. I
explain how to create and use them. I describe the
types of data that can be stored in variables and how to
store these different types. I also show you how to store
related data in complex variables called arrays.
Chapter 4
Using Variables in PHP Scripts
In This Chapter
Naming variables
Assigning values to variables
Removing variables
Using constants
Handling errors
Variables are containers that hold information. First, you give a variable a
name, and then you can store information in it. For example, you could
name a variable $age and store the number 21 in it. After you store information
in a variable, you can use that variable later in the script.
When using PHP on the Web, variables are often used to store the information
that users type into an HTML form, such as their names. You can then
use the variable later in the script, perhaps to personalize a Web page by displaying
the user’s name, as in, for example, Welcome Sam Smith.
In this chapter, you find out how to create variables, name them, and store
information in them. You also discover how to handle errors.
Naming Variables
Variable names or identifiers should be very descriptive. I have seen scripts
where all the variables were named $var1, $var1, $var2, and so on. It may
seem straightforward to name variables like this, but two years from now
when you come back to the script, it will take forever to figure out what
information is in each variable. PHP won’t care or get confused, but humans
trying to follow the script will have a hard time. Make your scripts much
easier to understand by using descriptive variable names like $firstName,
$directory_name, or $DateOfBirth.
The rules for variable names are as follows:
All variable names start with a dollar sign ($). This tells PHP that it is a
variable name.
Variable names can be any length.
Variable names can include letters, numbers, and underscores only.
Variable names must begin with a letter or an underscore. They
cannot begin with a number.
Uppercase and lowercase letters are not the same. $favoritecity
and $Favoritecity are not the same variable. If you store information
in $FavoriteCity, you can’t retrieve that information later in the script
by using the variable name $favoriteCity.
The following are valid variable names:
$_name
$first_name
$name3
$name_3
The following variable names cause error messages:
$3name
$name?
$first+name
$first.name
The first name is invalid because it doesn’t begin with a letter or an underscore,
as required. The three remaining names are invalid because they contain
characters other than numbers, letters, and underscores.
Assigning variable names is a matter of personal style. Creating descriptive
variable names by connecting words with an underscore or by using uppercase
letters to denote the beginning of new words (often called camel caps)
are the two most common variable naming styles, as shown here:
$first_name
$firstName
Naming your variables by using one of these two common styles makes it
easier for other programmers to read your scripts. It’s also common to start
the name with a lowercase letter. The most important factor in naming variables,
however, is to be consistent. Pick a style and use it throughout the
entire script.
54 Part II: Variables and Data
Assigning and Displaying
Variable Values
Variables can hold either numbers or strings of characters. A variable can
exist or not exist and can hold information or not hold information; these are
two separate ideas. Even if a variable doesn’t currently contain any information,
it still can exist, just as a drawer exists even when it is empty. Of course,
if a variable contains information, it has to exist.
The following sections discuss how to create variables, and how to assign
and display their values.
Creating variables
Storing information in a variable creates it.
To store information in a variable, you use a single equal sign (=). For example,
the following four PHP statements assign information to variables:
$age = 21;
$price = 20.52;
$temperature = -5;
$name = “Clark Kent”;
In these examples, notice that the numbers are not enclosed in quotes, but
the name, which is a string of characters, is. The quotes tell PHP that the
characters are a string, handled by PHP as a unit. Without the quotes, PHP
doesn’t know the characters are a string and won’t handle them correctly.
The different types of data and their uses are discussed in detail in Chapter 5.
Whenever you put information into a variable that did not previously exist,
you create that variable. For example, suppose you use the following PHP
statements at the top of your script:
$color = “blue”;
$color = “red”;
If the first statement is the first time you mention the variable $color, this
statement creates the variable and sets it to “blue”. The next statement
changes the value of $color to “red”.
55 Chapter 4: Using Variables in PHP Scripts
You can store the value of one variable in another variable, as shown in the
following statements:
$name1 = “Sally”;
$name2 = “Susan”;
$favorite_name = $name2;
After these statements are executed, the variable $favorite_name contains
the value “Susan”.
You can create a variable without storing any information in it. For example,
the following statement creates a variable:
$city = “”;
The variable now exists but does not contain any value. Chapter 5 contains a
discussion of the types of data that can be stored in a variable and their uses.
Displaying variable values
The quickest way to display the value stored in a variable is with the print_r
statement. You can output the value of a variable as in the following statements:
$today = “Sunday”;
print_r($today);
The output from the preceding statements is Sunday.
You can also display the value by using an echo statement. If you used the
following PHP statements
$age = 21;
echo $age;
in a PHP section, the output would be 21.
Using an echo statement of the preceding form, with one variable only, provides
the same basic output as the print_r statement. However, you can do
a lot more with the echo statement. You can output several items and include
numbers and strings together. For example, suppose the variable $name has
the value Clark Kent. You can include the following line in an HTML file:
<p>Welcome <?php echo $name ?></p>
The output on the Web page is as follows:
Welcome Clark Kent
56 Part II: Variables and Data
If you use a variable that does not exist, you get a warning message. For
example, suppose you intend to display $age, but type the following statement
by mistake:
echo $aeg;
You get a notice that looks like the following:
Notice: Undefined variable: aeg in c:\testvar.php on line 5
The notice points out that you’re using a variable that has not yet been given
a value. The notice is helpful in this case because it pinpoints your typo.
However, in some cases, writing a statement using a variable that does not
exist may not be a typo; you may be using the variable deliberately. For example,
you may be using it for a conditional statement (conditional statements
are described in Chapter 7.) The script may be running exactly the way you
want it to, and your only problem is the notice. You can prevent the notice
from being displayed by using @ before the variable name. If you don’t want
the notice to display, use the following statement:
echo @$aeg;
Because the @ turns off the error message and the variable doesn’t exist, the
echo statement displays nothing.
Don’t turn off any error message that you don’t understand. Be sure you
understand the error and are confident that it doesn’t affect your program
before you shut it off. The message may mean that your script has a problem
that needs to be fixed, such as the typo in the variable name shown in the
previous example.
Many languages require you to create a variable before you can use it. In
these languages, using a variable without creating it first is a fatal error, and
the script stops running. PHP, however, doesn’t require this, which may be
confusing if you have C or Java experience.
Writing Your First Script
That Uses Variables
In Chapter 3, the Hello World script displays Hello World! on a Web page
by using a simple echo statement. In this section, you write a script that also
displays Hello World!, but uses a variable in the script. In the script in
Chapter 3, the following PHP section is used to display the output:
57 Chapter 4: Using Variables in PHP Scripts
<?php
echo “<p>Hello World!</p>”;
?>
The following script is a complete script that contains a PHP section that
uses a variable to display Hello World!:
<html>
<head><title>Hello World Script using Variable</title></head>
<body>
<?php
$salutation = “Hello World!”;
echo “<p>$salutation</p>”;
?>
</body>
</html>
If you point your browser at this script by typing the URL into the browser,
the following output is displayed on the Web page:
Hello World!
A variable keeps its information for the whole script, not just for a single PHP
section. If a variable is set to 5 at the beginning of a script, it will still hold 5
at the end of the script (unless, of course, you assign it another value). For
example, the following script has two separate PHP sections:
<html>
<head><title>Hello World Script</title></head>
<body>
<?php
$salutation = “Hello World!”;
echo “<p>$salutation</p>”;
?>
<p>This is an HTML section</p>
<?php
echo “<p>$salutation again</p>”;
?>
</body>
</html>
If you point your browser at this script by typing the URL into your browser,
the following output displays on the Web page:
Hello World!
This is an HTML section
Hello World! again
58 Part II: Variables and Data
Discovering More about Output
Statements with Variables
In Chapter 3, echo statements are shown to have the following format:
echo outputitem1,outputitem2,outputitem3,…
You can use a variable for any output item. For example, you could write the
following PHP section:
<?php
$first_name = “Clark”;
$last_name = “Kent”;
echo “My name is “,$first_name,” “,$last_name;
?>
And the output of this section is the following:
My name is Clark Kent
Notice the space included between $first_name and $last_name. If this
space isn’t added, the output of the two variables runs together like this:
My name is ClarkKent.
Statements containing more than one variable must follow certain formatting
rules to produce the desired output. Table 4-1 shows some echo statements
containing variables and their output. The following variables are set for use
in the echo statements in the table:
$number = 123;
$word1 = “Hello”;
$word2 = “World!”;
Table 4-1 echo Statements with Variables
echo Statement Output
echo $number; 123
echo $word1,$word2; HelloWorld!
echo $word1,” “,$word2; Hello World!
echo $word1 $word2; Not valid because no commas separate
the variables; results in an error message
echo “$word1 $word2 now”; Hello World! now
59 Chapter 4: Using Variables in PHP Scripts
Notice that in line 2 of the table, there is no space between the two variable
names, so there is no space in the output. In line 3, a space is echoed between
the two variables.
In some echo statements, PHP can’t tell the variable name from the other
information around it. In cases where this could be confusing, you need to
enclose the variable name in curly braces. For example, suppose you use the
following statements:
$type = “bird”;
echo “Keep the $typecage clean”;
Rather than the desired output, you get the following message:
Notice: Undefined variable: typecage in testvar.php on line 6
After notifying you of the problem, the following output is displayed:
Keep the clean
To make this code work correctly, you need to use the following echo
statement:
echo “Keep the {$type}cage clean”;
With this statement, the output is the following:
Keep the birdcage clean
Using Variable Variables
PHP allows you to use dynamic variable names, called variable variables. You
can name a variable by using the value stored in another variable. That is, one
variable contains the name of another variable. For example, suppose you want
to construct a variable named $city with the value Los Angeles. You can use
the following statement:
$name_of_the_variable = “city”;
This statement creates a variable that contains the name that you want to
give to a variable. Then you use the following statements:
$$name_of_the_variable = “Los Angeles”;
Note the extra dollar sign ($) character at the beginning of the variable name.
This indicates a variable variable. This statement creates a new variable with
the name that is the value in $name_of_the_variable, resulting inthe
following:
60 Part II: Variables and Data
$city = “Los Angeles”;
The value of $name_of_the_variable does not change.
The following example shows how this feature works. In its present form, the
script statements may not seem that useful; you may see better ways to program
this task. The true value of variable variables becomes clear when they
are used with arrays and loops, as discussed in Chapters 6 and 7.
Suppose you want to name a series of variables with the names of cities that
have values that are the populations of the cities. You can use this code:
$Reno= 360000;
$Pasadena = 138000;
$cityname = “Reno”;
echo “The size of $cityname is ${$cityname}”;
$cityname = “Pasadena”;
echo “The size of $cityname is ${$cityname}”;
The output from this code is:
The size of Reno is 360000
The size of Pasadena is 138000
Notice that you need to use curly braces around the variable name in the
echo statement so that PHP knows where the variable name is. If you use the
statement without the curly braces, the output is as follows:
The size of Reno is $Reno
Without the curly braces in $$cityname, PHP converts $cityname to its
value and puts the extra $ in front of it, as part of the preceding string.
Removing Variables
You can also remove information from a variable. You can use the following
statement:
$age = __;
This takes the information out of the variable $age. It now has no value. This
does not mean that $age is set to 0. It means that $age is not storing any
information. Technically, it means that $age is storing a string of zero characters.
If you echo it, you get no error message or notice; it just echoes nothing,
a blank.
61 Chapter 4: Using Variables in PHP Scripts
You can go even further and uncreate the variable by using this statement:
unset($age);
After this statement, the variable $age no longer exists. If you try to echo it,
you get an “undefined variable” notice. You can unset more than one variable
at once, as follows:
unset($age,$name,$address);
Working with Constants
Constants are similar to variables. Constants are given names, and values are
stored in them. However, constants are constant; they can’t be changed by
the script. After you set the value for a constant, it stays the same. If you use
a constant for weather and set it to sunny, it can’t be changed. Wouldn’t that
be grand — only sunny days from now on?
Creating constants
Constants are set by using the define statement. The general format is as
follows:
define(“constantname”,”constantvalue”);
For example, to set a constant with the weather, use the following statement:
define(“WEATHER”,”Sunny”);
This statement creates a constant called WEATHER and sets its value to
“Sunny”.
When naming constants, use descriptive names, as you do for variables.
However, unlike variables, constant names do not begin with a dollar sign ($).
By convention, constants are given names that are all uppercase so you can
see easily that they’re constants. However, PHP accepts lowercase letters
without complaint.
You can store either a string or a number in a constant. The following statement,
which defines a constant named INTEREST and assigns to it the value
.01, is perfectly okay with PHP:
define (“INTEREST”,.01);
62 Part II: Variables and Data
Constants should not be given names that are keywords for PHP. Keywords are
words that have meaning for PHP, such as echo, and they can’t be used as constants
because PHP treats them as the PHP feature of the same name. PHP will
let you define a constant ECHO without giving an error message, but it will have
a problem when you try to use the constant. For example, if you use the following
statement:
echo ECHO;
PHP gets confused and displays an error message. It sees the constant as the
beginning of another echo statement, but it can’t find all the things it needs
to complete the first echo statement.
Some PHP keywords include the following:
63 Chapter 4: Using Variables in PHP Scripts
and
as
break
case
class
const
continue
declare
default
die
do
echo
else
empty
eval
exit
for
foreach
function
global
if
include
list
new
or
print
require
return
switch
use
var
while
If you’re baffled by some code that looks perfectly okay but refuses to work
correctly, even after numerous changes, try changing the name of a constant.
It’s possible that you are using an obscure keyword for your constant, and
that’s causing your problem. This doesn’t happen often, but it’s possible.
Although you can use keywords for variable names, because the beginning $
tells PHP the keyword is a variable name, you probably shouldn’t. It causes
too much confusion for the humans involved.
Understanding when to use constants
If you know the value of something won’t change during the script, use a constant.
Using a constant allows you to use a descriptive name, making the
script clearer. For example, PRODUCT_COST is much clearer than 20.50.
Using a constant allows you set the value once at the beginning of the script.
If this value ever needs to be changed, using constants allows you to change
it in only one place, instead of finding and changing the value in 20 different
places throughout the script. One change is better than 20. It’s less work and
lessens the likelihood of missing a place that needed to be changed, leading
to unknown and unseen havoc.
Using a constant ensures that the value won’t be changed accidentally somewhere
in the script, leading to the wrong value being used in statements later
in the script.
Suppose you have a script that must change money from one currency to
another by multiplying the dollar amount by the exchange rate. For example,
if the exchange rate from U.S. to Canadian dollars is 1.52, you can write the
following code:
<?php
$US_dollars = 20.00;
$CA_dollars = $US_dollars * 1.52;
?>
Now, suppose your script contains 40,000 lines of code and you need to convert
U.S. dollars to Canadian dollars in 50 different places in the script. So you use
the preceding code in 50 different places. Then you realize that the exchange
rate is likely to change every week, so you would need to go through this script
every week and change 1.52 to something else, manually, in 50 different places.
That’s a lot of work.
A better way to handle this is to put the exchange rate in a variable so you
could change it only in one place. You change your script to the following:
<?php
$rate = 1.52;
$US_dollars = 20.00;
$CA_dollars = $US_dollars * $rate;
?>
You set $rate at the beginning of the script. Then you can use the two lines
that convert the currency in all 50 parts of the script. This is clearly a better
option. When the rate changes, you need to change the rate in only one
place. For example, if the exchange rate changes to 1.53 next week, you just
change the first line of the script to the following:
$rate = 1.53;
This would work. However, $rate is not a very descriptive name. Remember
that your script is 40,000 lines of code and the 2 lines of code that convert
currency are used in 50 different places. Suppose somewhere in the middle of
64 Part II: Variables and Data
your script you need to add some code to compute interest. Suppose you
accidentally use the following code somewhere in the middle of your script:
$interest_rate = 20;
$rate = $interest_rate-1;
$amount = $principal * $rate;
All the places after this code will have a different value for rate; the 1.52 that
you set at the beginning of your script will be replaced by the 19 set by this
code. You can guard against this by using more descriptive variable names.
Or an even better option is to use a constant, as in the following script:
<?php
define(“RATE”,1.52);
$US_dollars = 20;
$CA_dollars = $US_dollars * RATE;
?>
Now you are using a constant, RATE, that can’t be changed in the script. If
you try to add the line
RATE = 20;
in the middle of your script, PHP won’t allow it. So, you won’t make the mistake
that you made with the variable.
Next week when the exchange rate changes to 1.53, you just edit your script
as follows:
<?php
define(“RATE”,1.53);
$US_dollars = 20;
$CA_dollars = $US_dollars * RATE;
?>
Of course, this would be even better if you used a more descriptive name,
such as the following:
define(“US_TO_CA”,1.52);
Keep in mind that mistakes that seem impossible to make when you’re looking
at a ten-line script, become entirely possible when you think in terms of
scripts with thousands of lines of code, especially scripts with more than one
programmer involved.
If you know the value of something won’t change during the script, use a
constant. If you need to manipulate the value somewhere in the script, use
a variable.
65 Chapter 4: Using Variables in PHP Scripts
Displaying constants
You can determine the value of a constant by using print_r as follows:
print_r(US_TO_CA);
You can also use a constant in an echo statement:
echo US_TO_CA;
When you echo a constant, you can’t enclose it in quotes. If you do, it echoes
the constant name rather than the value. You can echo the constant as shown
in the preceding example, or you can enclose it with parentheses. You can
build more complicated output statements by using commas, as in the following
example:
echo “The Canadian exchange rate is $”,US_TO_CA;
The output from this statement is the following:
The Canadian exchange rate is $1.52.
Notice that the dollar sign is inside the quoted string in the first output
string, not in the second output item as part of the constant name.
Utilizing built-in PHP constants
PHP has many built-in constants that you can use in your scripts. For example,
the constant _ _LINE_ _ has a value that is the line number where it is
used, and _ _FILE_ _ contains the name of the file in which it is used. (These
constants begin with two underscores and end with two underscores.) For
example, you can use the following statement:
echo _ _FILE_ _;
The output looks similar to the following:
c:\program files\apache group\apache\htdocs\testvar2.php
PHP has many other built-in constants. For example, E_ALL and E_ERROR are
constants you can use to affect how PHP handles errors. These constants are
explained in the next section.
66 Part II: Variables and Data
Handling Error Messages
PHP tries to be helpful when problems arise by providing error messages. It
provides the following types of messages:
Error message: You receive this message when the script has a problem
that prevents it from running. The script displays an error message and
stops running. The message contains as much information as possible to
help you identify the problem. The following is a common error message:
Parse error: parse error in c:\test.php on line 6
Often, you receive this error message because you’ve forgotten a semicolon,
a parenthesis, or a curly brace.
Warning message: You receive a warning message when the script sees
a problem but the problem does not prevent the script from running.
Warning messages do not mean the script can’t run; they indicate that
PHP believes something is probably wrong. You should identify the
source of the warning and then decide whether it needs to be fixed. It
usually does. For example, you see the following message if you don’t
include a variable name in the print_r statement — print_r() rather
than print_r($varname).
Warning: print_r() expects at least 1 parameter, 0 given
in d: test1.php on line 9
Because this is a warning, not an error, the script continues to execute
the statements after the print_r statement. However, a warning usually
indicates a more serious problem than a notice. In this case, you need to
fix the problem.
Notice: You receive a notice when PHP sees a condition that may be an
error or may be perfectly okay. One common condition that produces a
notice is echoing variables that don’t exist. Here’s an example of what
you might see in that instance:
Notice: Undefined variable: age in testing.php on line 9
Error messages, warning messages, and notices all indicate the filename causing
the problem and the line number where the problem was encountered.
The types of error messages that are displayed depend on the error level that
PHP is set to. You need to see all the error messages, but you may not want
to see all the warnings and notices. (Often the only problem with a notice is
the unsightly notice; the code is working correctly.) Or, you may want warning
messages and notices displayed during development but not after customers
are using the application. Or, you may want to send all the error messages to
a log file, rather than have them output for users to see.
67 Chapter 4: Using Variables in PHP Scripts
The next few sections tackle the subject of setting PHP to give you the type of
error messages that you want.
Changing the error level for your Web site
The error level for your Web site is defined in the php.ini file. You can
change the error level if you are the PHP administrator and have access to
the php.ini file. If you are not the administrator (which will be the case if,
for example, you are using a Web hosting company), you can change the
error level for each script, as described in the next section. (See Appendix A
for more on the php.ini file.)
To see what the current error level is, open php.ini in an editor and look for
a line similar to the following:
error_reporting = E_ALL; display all errors, warnings and
notices
This statement causes all errors, warnings, and notices to be displayed. This
setting is useful when you’re developing the script. However, when you
release the script for users, you probably don’t want notices displayed.
In the preceding example, notice that there is a semicolon (;) after E_ALL but
not at the beginning of the line. The semicolon is the character that indicates
a comment in the php.ini file. Therefore, the text on the line after the semicolon
is just a comment, not part of the statement. If there were a semicolon
at the beginning of the line, the entire line would be a comment, and the
statement would not be in effect.
When you look in your php.ini file, you will probably find several statements
like the preceding line, except with semicolons at the beginning of the lines.
These statements are included as examples, not as statements that execute.
Look for the statement without a semicolon in front of it to see which statement
is currently active.
E_ALL is a built-in PHP constant that refers to all errors, warnings, and
notices. E_NOTICE is a built-in constant representing notices. You can use
these two constants in the following statement:
error_reporting = E_ALL & ~E_NOTICE
E_ALL tells PHP to display all errors, warnings, and notices. However, the
second term ~E_NOTICE tells PHP not to display notices. The result is that
only errors and warnings are displayed. This method of specifying the errors
to be displayed is shorter than listing all the types of errors that you want to
display.
68 Part II: Variables and Data
The two statements shown in this section are used most often. You can use
other constants to specify error levels, but E_ALL and E_NOTICE are usually
sufficient for most scripts. You can find a listing of all the constants in the
php.ini file. For a complete discussion of error levels, check out the PHP
online manual.
You can stop error reporting all together. You may not want users to see any
of the PHP-generated error or warning messages because they may contain
compromising information. Usually if you do this, you want to save error
messages in a log instead, as described later in this chapter in the section,
“Sending messages to a log.”
To turn off error reporting, find the line that says display_errors = On in
php.ini and change On to Off.
You need to restart your Web server before any changes you make in
php.ini will go into effect.
Changing the error level for a script
If you want to set the error level for a particular script, add a statement with
the following format to the beginning of the script:
error_reporting(OPTIONS);
The OPTIONS in the statement are the built-in constants discussed in the preceding
section. For example, you can have all errors, warnings, and notices
displayed in the script by adding the following statement:
error_reporting(E_ALL);
Suppose the setting in php.ini is set to E_ALL. You may be satisfied with
that level while developing your scripts, but then want to stop displaying
notices when users start running your scripts. To override the php.ini setting,
you can add the following statement to the scripts after they are finetuned
and ready to go:
error_reporting(E_ALL & ~E_NOTICE);
You can set error reporting so that no messages are displayed by using the
following statement:
error_reporting(0);
69 Chapter 4: Using Variables in PHP Scripts
Sometimes you want to turn error and warning messages off when your
scripts are complete and being used by the world. You may not want users to
see the error messages that PHP sends because the information in the PHP
messages can represent a security issue, but you may want to see any error
messages from PHP yourself. You can turn error reporting off by using a setting
of zero, but log the error messages to a file at the same time. Users don’t
see the messages, but you can look at them. Sending messages to a log is
described in the next section.
Sending messages to a log
You can send the errors and warnings from PHP to a log file. You may want to
have a permanent record of errors as well as display them, or you may want
to send the errors to a file rather than display them for the world to see.
You can set up an error message log for the whole site by using settings in
the php.ini file, if you have access to it. Open php.ini and find the following
line:
log_errors = Off
You need to change Off to On. You also need to tell PHP where to send the
error messages. To do this, find the following line:
;error_log = filename
Now remove the semicolon from the beginning of the line. This changes the
line from a comment to a statement. Change filename to the path to the file
into which you want the messages saved. For example, you could use the following
statement:
error_log = c:\temp\php_error_log
The directory (often called folder in Windows) must exist. For this statement,
you must create the directory c:\temp before the error messages can be
logged there. You don’t need to create the file; PHP can create the file as long
as it can find the directory.
You need to restart your Web server before any changes you make in
php.ini will go into effect.
Advanced error handling
This section describes advanced error handling. Newbies do not need to read
this section. Come back and read this section after you have some experience
with the programming techniques described in the rest of the book.
70 Part II: Variables and Data
The standard PHP errors and error messages may not be sufficient for your
needs. For example, you may know something is an error in your script,
although PHP sees nothing wrong with the problem. For example, you may
be writing a script to design a house. In such a case, if $height_of_door is
larger than $height_of_house, you know that something is wrong. You know
this, but PHP doesn’t. PHP would not recognize this as an error condition. To
get PHP to check for this error in the script, you could write the following
statement:
If ($height_of_door > $height_of_house)
{
trigger_error(“Impossible condition”,E_USER_ERROR);
}
Using if statements is explained in detail in Chapter 7.
The E_USER_ERROR in the statement tells PHP that the condition is an error.
The string “Impossible condition” is the message to be displayed when the
error is encountered. If the condition is true, the following message is displayed:
Fatal error: Impossible condition in d:\testerr.php on line 9
The script stops at this point because you told PHP that it was an error,
rather than a warning or a notice. You can use E_USER_WARNING or
E_USER_NOTICE, rather than E_USER_ERROR, to have PHP treat the condition
as a warning or notice.
If you want to handle the error in your own way, instead of using PHP standard
error procedures, you can write your own statements to perform actions, such
as send a message, log a message, send an e-mail, or stop the script. For example,
you could simply echo an error message to the user and stop the script, as
follows:
If ($height_of_door > $height_of_house)
{
echo “This is impossible<br>”;
exit();
}
If $height_of_door is larger than $height_of_house, the message is
echoed, and exit() stops the script. No more statements are executed.
You could also send a message to a PHP error log when this condition occurs
by using the following type of statement:
error_log(message,3,logfilename);
For example, you could use the following if block:
71 Chapter 4: Using Variables in PHP Scripts
If ($height_of_door > $height_of_house)
{
error_log(“The door is taller than the
house”,3,”/temp/err_log”);
exit();
}
After this statement, if $height_of_door is larger than $height_of_house,
the message “The door is taller than the house” is stored in the log
file /temp/err_log. The 3 in the statement tells PHP to store the message in
the specified log file. The directory /temp must exist, but PHP will create the
file if it doesn’t already exist.
Alternatively, you might want to send yourself an e-mail message when the
error occurs. The error_log statement can be used for this purpose as well
as for logging an error message. The 1 in the following error_log statement
tells PHP to send the message as e-mail to the specified e-mail address:
error_log(“The door is taller than the
house”,1,”me@mymail.com”);
This statement assumes that e-mail can be accessed from PHP. See the discussion
of PHP and e-mail in Chapter 13.
On the other hand, you may be willing to accept PHP’s definition of an error,
but want it to behave differently when it encounters an error. You could have
procedures you want performed in the event of an error. You may want PHP
to display a message written by you or to execute statements written by you.
For example, you may want to be informed by e-mail of error messages, or
you may want certain files opened or closed before the script stops.
You can write your own code to handle errors and instruct PHP to use your
code whenever it encounters an error. To do this, you write your own errorhandling
code and save it as a function, which is a piece of code you write
and call repeatedly whenever you need it. (Instructions for writing functions
are provided in Chapter 8.) You can tell PHP to use your function rather than
its own procedure for error handling by using the following statement:
set_error_handler(functionname);
For example, you could use the following:
set_error_handler(my_error_handler);
Further instructions for writing my_error_handler are provided in Chapter 8
where functions are discussed.
Another method for handling errors recognized by PHP is to use the die
statement to display a message when a function fails. The die statement is
discussed in detail in Chapter 8 along with the discussion of functions.
72 Part II: Variables and Data
Chapter 5
Working with Data
In This Chapter
Understanding data types
Performing arithmetic
Manipulating character strings
Using dates and times
Variables can store data of different types, and different types of data can
do different things. For example, you can add variables whose values are
numbers (1 + 2), but adding variables whose values are characters (a + b)
doesn’t make much sense. In this chapter, you find out what data types PHP
can handle and how you can use them.
Understanding Data Types
You can store the following simple types of data in PHP variables:
Integer: A whole number (no fractions), such as –43, 0, 1, 27, or 5438.
The range of integers that is allowed varies, depending on your operating
system, but in general, you can usually use any number from
–2 billion up to +2 billion.
Floating point number: A number (usually not a whole number) that
includes decimal places, such as 5.24 or 123.456789. This is often called
a real number or a float.
Character string: A series of single characters, such as hello. There is
no practical limit on the length of a string.
Boolean: A TRUE or FALSE value. See the nearby sidebar for more
information.
Assigning data types
Most other languages require that you initialize the variable before using
it, specifying what type of data it can hold, but PHP is more informal. You
don’t need to tell PHP which data type is in a variable. PHP evaluates the
data when you assign it to the variable and then stores it as the appropriate
type. Generally, this is helpful. PHP guesses the data type pretty accurately.
PHP also converts data when it needs to be converted. For example, if you
have the following statements, PHP converts the data types with no problem:
$firstNumber = 1; # PHP stores it as an integer
$secondNumber = 1.1; # PHP stores it as a float
$sum = $firstNumber + $secondNumber;
Technically, the third statement is not possible because the data to be added
are different types. However, PHP converts the integer to a float so that the
addition proceeds smoothly. This happens automatically and invisibly and is
very helpful.
Type casting
On a rare occasion, PHP guesses badly when it stores the data. You might
need to do something with a variable, and PHP won’t let you because the
74 Part II: Variables and Data
True or false? Boolean values
Boolean data types represent two possible
states — TRUE or FALSE. Boolean values are
used mainly to compare conditions for use in
conditional statements. For example, PHP evaluates
an expression, such as $a > $b, and the
outcome is either TRUE or FALSE.
PHP considers the following values FALSE :
The string FALSE (can be upper- or
lowercase)
The integer 0
The float 0.0
An empty string
The one-character string 0
The constant NULL
Any other values in a Boolean variable are considered
TRUE. If you echo a Boolean variable,
the value FALSE displays as a blank string; the
value TRUE echoes as a 1. Functions often
return a Boolean variable that you can test to
see whether the function succeeded or failed.
For more information on using Boolean variables
with functions, check out Chapter 8.
data is the wrong type. In such a case, you can specify how you want PHP to
store the data, rather than let PHP decide for itself. This is called type casting.
To specify a particular type, use a statement like one of the following:
$newint = (int) $var1;
$newfloat = (float) $var1;
$newstring = (string) $var1;
The value in the variable on the right side of the equal sign is stored in the
variable on the left side as the specified type. So the value in $var1 is stored
in $newint as an integer, as specified by (int).
Be careful when doing type casts. Sometimes you can get unexpected results.
For example, when you cast a float into an integer, it loses its decimal places.
To do this, PHP rounds the float toward 0. For example, if $number = 1.8
and you cast it into an integer — $newnumber = (int) $number —
$newnumber will equal 1.
You can find out the data type of a variable by using a statement like the
following:
var_dump($myvariable);
For example, the following statement checks the data type of $checkvar:
var_dump($checkvar);
The output from this statement is int(27), which tells you that $checkvar
contains the integer 27.
Working with Numbers
The data types float and integer are both numbers. You store them in variables
as follows:
$intvar = 3;
$floatvar = 9.3;
PHP automatically stores the values as the correct data type.
Performing mathematical operations
PHP allows you to do mathematical operations on numbers. You indicate
mathematical operations by using two numbers and a mathematical operator.
75 Chapter 5: Working with Data
For example, one operator is the plus (+) sign, so you can indicate a mathematical
operation like this:
1 + 2
You can also do math with variables:
$var1 + $var2;
If you plan to use numbers in mathematical operations, don’t enclose them in
quotes when assigning them to variables. Using quotes sets the numbers as
character strings, and you can’t perform mathematical operations on character
strings. However, PHP, as opposed to most other languages, will automatically
convert strings to numbers when it needs to. For example, suppose you
have the following statements:
$var1 = “1”;
$var2 = 2;
$total = $var1 + $var2;
Technically, you can’t add these two numbers together because $var1 is a
character string. However, PHP automatically converts the string 1 to a
number 1 when it gets to the third statement and then adds the numbers.
If you use the following statements, PHP also converts the string so it can add
the numbers, but the results are not as obvious:
$var1 = “x”;
$var2 = 2;
$total = $var1 + $var2;
Because x is not a number that PHP can convert, it uses 0 in the addition. The
result is that $total equals 2. In most cases, this conversion is not what you
want. The automatic conversion feature is useful, and saves some typing, but
be careful when depending on it. Sometimes you don’t get the results you
expect, as shown in the previous example.
PHP can also guess wrong because it doesn’t understand certain human notation.
For example, the following statements cause PHP to get it wrong:
$var1 = “2,000”;
$var2 = 2;
$total = $var1 + $var2;
76 Part II: Variables and Data
Although people understand what commas mean in numbers, PHP does not.
PHP thinks 2,000 ends at the comma. After these statements are executed,
$total equals 4.
Table 5-1 shows the mathematical operators that you can use.
Table 5-1 Mathematical Operators
Operator Description
+ Adds two numbers together.
- Subtracts the second number from the first number.
* Multiplies two numbers together.
/ Divides the first number by the second number.
% Finds the remainder when the first number is divided by the second
number. This is called modulus. For example, in $a = 13 % 4, $a
is set to 1.
Understanding the order of operations
You can do several mathematical operations at once. For example, the following
statement performs three operations:
$total = 1 + 2 * 3 + 1;
The order in which the arithmetic is performed is important. You can get different
results depending on which operation is performed first. PHP does
multiplication and division first, and then addition and subtraction. If other
considerations are equal, PHP goes from left to right. Consequently, the preceding
statement sets $total to 8, in the following order:
$total = 1 + 2 * 3 + 1 #first, it does the multiplication
$total = 1 + 6 + 1 #next, it does the leftmost addition
$total = 7 + 1 #next, the remaining addition
$total = 8
You can change the order in which the arithmetic is performed by using
parentheses. The arithmetic inside the parentheses is performed first. For
example, you can write the previous statement with parentheses, like this:
$total = (1 + 2) * 3 + 1;
77 Chapter 5: Working with Data
This statement sets $total to 10, in the following order:
$total = (1 + 2) * 3 + 1 #first, the math in the parentheses
$total = 3 * 3 + 1 #next, the multiplication
$result = 9 + 1 #next, the addition
$result = 10
The general order of operations is in force inside of parentheses when there
is more than one operation, such as (3 + 2 * 5). In this example, the multiplication
is performed first. You can use parentheses inside of parentheses to
change that order as well.
On the better-safe-than-sorry principle, it’s best to use parentheses whenever
more than one answer is possible.
Incrementing and decrementing
PHP provides a shortcut for adding 1 to a variable. If you want to add 1 to a
variable, you can use a statement like the following:
$counter=$counter+1;
PHP also lets you write a shorter statement that does the same thing:
$counter++;
For example, you could use the following statements:
$counter=0;
$counter++;
echo $counter;
This echo statement outputs 1, because ++ adds 1 to the current value of
$counter. You can also subtract 1 by using the following statement:
$counter–;
Another shortcut for adding a number to an existing variable is +=1, which
adds 1 to the variable. You can add any number to a variable by using this
shortcut. You can also subtract, multiply, or divide by using a similar shortcut.
The following are some valid statements using this shorter format:
$counter+=2;
$counter-=3;
$counter*=2;
$counter/=3;
78 Part II: Variables and Data
These statements add 2 to $counter, subtract 3 from $counter, multiply
$counter by 2, and divide $counter by 3, respectively.
Using built-in higher-math functions
PHP provides functions to perform more complicated math for you. (Functions
are described further in Chapter 8.) For example, if you need to compute a
square root, you don’t have to write code that does all the math. PHP has
already written this code for you. You can just use a statement like one of
these:
$rootvar = sqrt(91);
$rootvar = sqrt($number);
The first statement takes the square root of a number, and the second statement
takes the square root of a variable’s value.
You can use a statement like the following to round up to the next integer:
$upnumber = ceil(27.63);
The result is 28. You can also round down by using the following format:
$downnumber = floor(27.63);
The result of this segment is 27.
PHP offers many math functions, including functions for simple math, such as
maximum, minimum, and random numbers; and functions for advanced math,
such as sine, tangent, and converting to binary or octal numbers. To find a particular
mathematical function, see Appendix B.
Formatting numbers for output
Often you want to display a number in a familiar format, such as with commas
dividing the thousands or formatted as dollar amounts with two decimal places.
But PHP stores and displays numbers in the most efficient format. If the number
is 10.00, it is displayed as 10. Therefore, you need to tell PHP how you want the
number displayed.
One PHP statement that formats numbers is the number_format statement,
which has the following general form:
number_format(number,decimals,”decimalsep”,”thousandsep”)
79 Chapter 5: Working with Data
In this format, each piece of input has a meaning:
number is the number to be formatted. This must always be included.
decimals is the number of decimal places. If decimals is not included,
the number of decimal places is 0 by default, and number is rounded
to the closest integer. If you are going to include thousandsep and
decimalsep, you must include decimals.
decimalsep is the character used to separate the decimal places. The
default is a decimal point. If you include this, you must also include
thousandsep.
thousandsep is the character used to separate the number into thousands.
The default is a comma. If you include this parameter, you must
also include decimalsep.
Table 5-2 shows some number_format statements and their output.
Table 5-2 number_format Statements
$number Format Output
12321 number_format($number) 12,321
12321.66 number_format($number,2) 12,321.66
12321.66 number_format($number) 12,322
12321.6 number_format($number,3) 12,321.600
12321 number_format($number,0,”.”,”.”) 12.321
12321.66 number_format($number,2,”.”,””) 12321.66
After formatting, the number is converted to a string data type, so perform
any arithmetic on the number before you format it.
For more complicated formatting, PHP provides the statements printf and
sprintf:
printf outputs the formatted number directly.
sprintf is used to store the formatted number into a variable.
The formatting statements printf and sprintf can be used to format character
strings as well as numbers, and to output strings and numbers in the
same output statement. For a more complete description of these statements,
check out the section “Formatting output strings,” later in this chapter.
80 Part II: Variables and Data
Working with Character Strings
Characters are letters, numbers, and punctuation, and a character string is a
series of characters. When a number is used as a character, it is just a stored
character, the same as a letter. It can’t be used in arithmetic. For example, a
phone number usually is stored as a character string and not a number
because it only needs to be stored, not added or multiplied.
When you store a character string in a variable, you use double quotes or
single quotes to tell PHP where the string begins and ends. For example, the
following two statements are the same:
$string = _Hello World!_;
$string = _Hello World!_;
81 Chapter 5: Working with Data
Storing really long strings
PHP provides a feature called a heredoc that is
useful for assigning values to really long strings
that span several lines. A heredoc enables you
to tell PHP where to start and end reading a
string. A heredoc statement has the following
format:
$varname = <<<ENDSTRING
text
ENDSTRING;
ENDSTRING is any string you want to use. You
enclose the text you want stored in the variable
$varname by typing ENDSTRING at the beginning
and again at the end. When PHP processes
the heredoc, it reads the first ENDSTRING and
knows to start reading text into $varname. It
continues reading text into $varname until it
encounters the same ENDSTRING again. At
that point, it ends the string.
The string created by a heredoc statement
evaluates variables and special characters in
the same manner as a double-quoted string.
(For details on double-quoted strings, see the
section, “Comparing single-quoted strings and
double-quoted strings,” later in this chapter.)
The following statements create a string by
using the heredoc method:
$distance = 10;
$herevariable = <<<ENDOFTEXT
The distance between
Los Angeles and Pasadena
is $distance miles.
ENDOFTEXT;
echo $herevariable;
The output of the echo statement is as follows:
The distance between Los
Angeles and Pasadena is 10
miles.
But be careful. PHP is picky about its ENDSTRINGs.
When it first appears, the ENDSTRING
(ENDOFTEXT in this example) must
occur at the end of the first line, with nothing following
it, not even a space. And the ENDSTRING
on the last line must occur at the start
of the line, with nothing before it, not even a
space, and nothing following it other than the
semicolon. If these rules are broken, PHP won’t
recognize the ending string and will continue
looking for it throughout the rest of the script. It
will eventually display a parse error showing a
line number that is the last line in the script.
Using special characters in strings
PHP provides some special characters you can use in strings: \n and \t. You
can use \n to start a new line in a string, as in the following statements:
$string = “Hello \nWorld”;
echo $string;
The output is broken into two lines:
Hello
World
You can use \t to insert a tab, as in the following statements:
$string = “Line 1 \n\tLine 2”;
echo $string;
The second line of the output is indented:
Line 1
Line 2
Special characters can be used only in strings enclosed with double quotes.
In single-quoted strings, special characters have no special meaning; they are
output the same way as any other character. The difference between single
and double quotes is explained in the next section.
Comparing single-quoted strings
and double-quoted strings
Single-quoted and double-quoted strings are handled differently:
Single-quoted strings are stored literally, with the exception of \’, which
is stored as an apostrophe. (For more information about \’, see the next
section, “Escaping characters.”)
In double-quoted strings, variables and special characters are evaluated
before the string is stored.
The following examples show the difference in output produced by single and
double quotes.
If you enclose a variable in double quotes, PHP uses the value of the variable.
However, if you enclose a variable in single quotes, PHP uses the literal variable
82 Part II: Variables and Data
name. For example, the following statements use both the single and double
quote methods with a variable:
$name = “Sam”;
$output1 = _$name_;
$output2 = _$name_;
echo $output1;
echo $output2;
The output of these echo statements is as follows:
Sam
$name
If you use special characters in a string enclosed by double quotes, PHP outputs
the string after evaluating the special characters. However, if you enclose
the string in single quotes, PHP outputs the special characters as literals. For
example, the following statements use both single and double quotes with the
new line character \n and the tab character \t:
$string1 = “String in \n\tdouble quotes”;
$string2 = ‘String in \n\tsingle quotes’;
When $string1 is displayed, you get the following:
String in
double quotes
When $string2 is displayed, you get the following:
String in \n\tsingle quotes
The quotes that enclose the entire string determine the treatment of variables
and special characters, even if there are other sets of quotes inside the string.
For example, look at the following statements:
$number = 10;
$string1 = “There are ‘$number’ people in line.”;
$string2 = ‘There are “$number” people waiting.’;
echo $string1,”\n”;
echo $string2;
The output is as follows:
There are ‘10’ people in line.
There are “$number” people waiting.
83 Chapter 5: Working with Data
You can see that even though $number is enclosed in single quotes in
$string1, the double quotes around the entire string cause the output to
contain the value of the variable rather than the name of the variable.
Similarly, even though $number is enclosed in double quotes in $string2,
the single quotes around the entire string cause the output to contain the
name of the variable rather than the value of the variable
Escaping characters
Sometimes you want a character in a double-quoted string to be treated as a
literal, not as a special character, even though it has special meaning. For
example, you may want to output a dollar sign as a dollar sign, rather than
have the dollar sign treated as the first character of a variable name. You can
tell PHP to output characters, rather than use their special meaning, by preceding
the character with a backslash (\). This is called escaping the character.
For example, the following two strings produce the same output:
$string = ‘The variable name is $var1’;
$string = “The variable name is \$var1”;
The output from either string is the following:
The variable name is $var1
Suppose you want to store a string as follows:
$string = _Where is Sally_s house_;
echo $string;
These statements won’t work because when PHP sees the ‘ (single quote)
after Sally, it thinks this is the end of the string. It displays the following:
Where is Sally
You need to tell PHP to interpret the single quote (‘) as an apostrophe, not as
the end of the string. You can do this by using a backslash (\) in front of the
single quote. The backslash tells PHP that the single quote does not have any
special meaning; it’s just an apostrophe. To display the string correctly, use
the following statement:
$string = _Where is Sally\_s house_;
When you enclose a string in double quotes, you must also use a backslash in
front of any double quotes inside the string.
84 Part II: Variables and Data
Joining strings together
You can join strings together, a process called concatenation, by using a dot
(.). For example, you can join $string1 and $string2 with the following
statements:
$string1 = _Hello_;
$string2 = _World!_;
$stringall = $string1.$string2;
echo $stringall;
The echo statement outputs one string:
HelloWorld!
Notice that no space appears between Hello and World!. That’s because no
spaces are included in the two strings that are joined. You can add a space
between the words by joining three strings together — the two variables and
a string that contains a single space — with the following statement rather
than the earlier statement:
$stringall = $string1._ _.$string2;
You can use .= to add characters to an existing string. For example, you can
use the following statements, in place of the preceding statements:
$stringall = “Hello”;
$stringall .= “ World!”;
echo $stringall;
The echo statement outputs this:
Hello World!
Manipulating strings
PHP provides many built-in functions for manipulating strings. (Functions
are discussed in detail in Chapter 8.) Using PHP functions, you can find substrings
or characters, replace part of a string with different characters, take a
string apart, count the length of a string, and perform many other string
manipulations.
85 Chapter 5: Working with Data
Often you want to remove blank spaces before or after a string. You can
remove leading or trailing spaces by using the following statements:
$string = trim($string) # removes leading & trailing spaces
$string = ltrim($string) # removes leading spaces
$string = rtrim($string) # removes trailing spaces
PHP can help you split a string into words, which is often handy. The general
form of this function is as follows:
str_word_count(“string”,format)
In this expression, format can be 1, meaning return the words as a numeric
array; or 2, meaning return the words as an array where the key is the position
of the first character of the word. (Arrays are explained in Chapter 6.) If
you don’t include a format, the function returns the number of words. The
following examples use str_word_count:
$string = “Counting Words”;
$numberOfWords = str_word_count($string);
$word1 = str_word_count($string,1);
$word2 = str_word_count($string,2);
After the statements are executed, the following variables exist:
$numberOfWords = 2
$word1[0] = Counting
$word1[1] = Words
$word2[0] = Counting
$word2[9] = Words
Notice that the first word starts at position 0 (not position 1 as you and I
might think), and the next word starts at position 9. I explain this more fully
in Chapter 6 when I discuss arrays.
Some additional useful string manipulation statements are shown in Table 5-3
with examples. When looking at the examples, remember that the first position
in the string is 0, not 1.
86 Part II: Variables and Data
Table 5-3
String Manipulation
Function Format
What It Does
Example
Result
str_repeat(“str”,n)
Repeat str
n
times
$x=str_repeat(“x”,5);
$x=xxxxx
str_replace(“a”,”b”,
Replace all a
$a=”abc abc”;
$s=
”str”)
with b
in str
$s=str_replace(“b”,”i”,$a);
aic aic
strchr(“string”,
Returns string
$str=”aBc abc”;
$sub=bc
”char”);
from char
to end
$sub=strchr($str,”b”);
stristr(“string”,
Same as strchr,
$str=”aBc abc”;
$sub=
”char”);
except not case sensitive
$sub=stristr($str,”b”);
Bc abc
strlen(“string”)
Returns length of string
$n=strlen(“hello”);
$n=5
strpos(“string”,
Returns position of first
$str=”hello”;
$n=2
”substr”)
substr
beginning
$n=strpos($str,”ll”);
strrchr(“string”,
Same as strchr, except
$str=”abc abc”;
$sub=bc
”char”);
finds only the last instance of char
$sub=strrchr($str,”b”);
strrev(“string”)
Reverses string
$n=strrev(“abcde”);
$n=edcba
strrpos(“string”,
Returns position of last
$str=”abc abc”;
$n=5
”substr”)
instance of substr
$n=strrpos($str,”bc”);
strtolower(“string”)
Returns a lowercase version of string
$str=strtolower(“YES”);
$str=yes
(continued)
87 Chapter 5: Working with Data
Table 5-3
(continued)
Function Format
What It Does
Example
Result
strtoupper(“string”)
Returns an uppercase version of string
$str=strtoupper(“yes”);
$str=YES
Replaces all str1
with
$str=”aa bb cc”;
$new=
”str1”,”str2”)
str2
in string
$new=strtr($str,”bb”,”xx”);
aa xx cc
substr(“string”,n1,n2)
Returns string
$sstr=substr(“hello”,2,4);
$sstr=llo
between n1
and n2
substr_count(“str”,
Returns the number of
$str=”abc ab abc”;
$n=2
”sub”)
occurrences of sub
in str
$s=”bc”;$n=substr_count($str,$s);
substr_replace(“s”,
Replace r
into s, beginning
$s=”abc abc”;
$t=
”r”,n,l)
with n
for l
characters
$t=
abxbc
substr_replace($s,”x”,2,3);
ucfirst(“string”)
Changes first letter of
$str=”a B c”;
$str2=
string
to uppercase
$str2=ucfirst($str);
A B c
ucwords(“string”)
Changes each word of
$str=”aa Bb cc”;
$str2=
string
to uppercase
$str2=ucwords($str);
Aa Bb Cc
88 Part II: Variables and Data
Formatting output strings
The output produced by PHP is always in string format. That is, the output of
the echo statement is a string, even if the output statement included a variable
containing a number. The following is an output statement:
$number = 4;
echo “Sally has $number children.”;
The output is as follows:
Sally has 4 children.
The output is a string, even though 4 was a number when it was in the variable
named $number. The echo statement outputs 4 as part of a character
string.
Formatting the output is an important part of scripting. The echo statement
allows quite a bit of flexibility in formatting output. In the section, “Formatting
numbers for output,” earlier in this chapter, I describe some possibilities for
formatting numbers by using the number_format statement. PHP provides
additional statements for formatting output strings. The printf and sprintf
statements allow you to format strings, numbers, and a mix of both strings
and numbers.
The general format is as follows:
printf(“format”,$varname1,$varname2,. . .);
$newvar = sprintf(“format”,$varname1,$varname2,. . .);
The printf statement outputs formatted strings; sprintf stores the formatted
output in a variable. You can format strings or numbers or both together,
including variable values. The information in format gives instructions for
the format, and $varname contains the value(s) to be formatted. The following
statement is valid:
$newvar = sprintf(“Hello World!”);
This statement outputs the literal string, as given, because no format is
included. The string “Hello World!” is now assigned to the variable $newvar.
However, you can mix variables with literals by using the following statements:
$nboys = 3;
$ngirls = 2;
printf(“%s boys and %s girls”,$nboys,$ngirls);
89 Chapter 5: Working with Data
The %s is a formatting instruction that tells printf to insert the variable
value as a string. Thus, the output is: 3 boys and 2 girls. The % character
signals printf that a formatting instruction starts here. The formatting
instruction has the following format:
%pad-width.dectype
These are the components of the formatting instructions:
%: Signals the start of the formatting instruction.
pad: A padding character that is used to fill out the string when the value
to be formatted is smaller than the width assigned. (See width, later in
this list.) If you don’t specify a character, a space is used. pad can be a
space, a 0, or any character preceded by a single quote (‘). For example,
it is common to pad numbers with 0 — for example, 01 or 0001.
-: A symbol meaning to left-justify the characters. If this is not included,
the characters are right-justified.
width: The number of characters to use for the value. If the value doesn’t
fill the width, the padding character is used to pad the value. For example,
if the width is 5, the padding character is 0, and the value is 1, the output
is 00001.
.dec: The number of decimal places to use for a number. This value is
preceded by a decimal point.
type: The type of value. Use s (string) for most values. Use f (float) for
numbers that you want to format with decimal places.
The following are some possible sprintf statements:
$money = 30;
$pet = “Kitten”;
$new = sprintf(“It costs $%03.2f for a %s.\n”,$money,$pet);
$new2 = sprintf(“%’.-20s%3.2f”,$pet,$money);
echo $new;
echo $new2;
The output of these statements is
It costs $030.00 for a Kitten.
Kitten………….. 30.00
Notice that the format for $money is 3.2f (3 digits wide with 2 decimal places)
for both $new and $new2, but in $new, it’s padded with a 0. In $new2, the
number format is not padded, so there is a space before 30.
For $new2, the format for $pet is ‘.-20. The 20 makes the space for $pet
20 characters wide. The value Kitten takes up 6 characters. The format characters
‘. tell sprintf to pad the space with dots, so that produces 14 dots.
90 Part II: Variables and Data
The – format character says to left justify Kitten, so Kitten is on the left side
of the space, and the padding comes after Kitten. If the – is left out, Kitten is
right justified by default, which means that Kitten is on the right side of the
space, with the dots coming before it.
Often scripts need to display columns of numbers. For example, you might
have three numbers: 12.3, 1, and 234.55. If you just echo them, they display
as follows:
12.3
1
234.55
Even if you use number_format to specify two decimal places, they display
as follows:
12.30
1.00
234.55
You can display them in an orderly column, however, by using printf as
follows:
printf(“%5.2f\n”,$number1);
printf(“%5.2f\n”,$number2);
printf(“%5.2f\n”,$number3);
Your output is as follows:
12.30
1.00
234.55
In the preceding statements, %5.2f\n is the format that tells PHP how to
format the number in the output. Here’s a closer look:
%: Tells PHP that the following digits are a formatting instruction.
5: The width — how long the number should be. If the number is less
than 5 digits wide, it is right-justified, which means it’s moved as far right
as it can go. Right-justified is the default, so no symbol is needed in the
format to right-justify the numbers.
.2: Means that the number should be displayed with 2 decimal places.
f: Tells PHP to display the number as a float.
\n: Tells PHP to start a new line.
To put numbers into the proper format for dollars, you can use sprintf. The
following statement formats a number into a dollar amount:
$newvariablename = sprintf(“$%.2f”, $oldvariablename);
91 Chapter 5: Working with Data
This statement reformats the number in $oldvariablename and stores it in
the new format in $newvariablename. For example, the following statements
display money in the correct format:
$price = 25;
printf(“$%.2f”,$price);
You see the following output:
$25.00
Working with Dates and Times
Dates and times can be important elements in a script. PHP has the ability to
recognize dates and times and handle them differently than plain character
strings. The computer stores dates and times in a format called a timestamp,
which is expressed entirely in seconds. However, because this is an impractical
format for humans to read, PHP converts dates from your notation into a
timestamp the computer understands and from a timestamp into a format that
is familiar to people. PHP handles dates and times by using built-in functions.
The timestamp format is a UNIX Timestamp, an integer that is the number of
seconds from January 1, 1970 00:00:00 GMT to the time represented by the
timestamp. This format makes it easy to calculate the time between two
dates — just subtract one timestamp from the other.
Formatting dates
The function you will use most often is date. The date function converts a
date or time from the timestamp format into a format you specify. The general
format is as follows:
$mydate = date(“format”,$timestamp);
$timestamp is a variable with a timestamp stored in it. You previously stored
the timestamp in the variable by using a time or mktime, as described in the
next section. If $timestamp is not included, PHP obtains the current time
from the operating system. Thus, you can get today’s date with the following
statement:
$today = date(“Y/m/d”);
If today is March 10, 2004, this statement returns:
2004/03/10
92 Part II: Variables and Data
The format is a string that specifies the date format you want stored in the
variable. For example, the format “y-m-d” returns 04-3-10, and “M.d.Y”
returns Mar.10.2004. Table 5-4 lists some of the symbols that you can use in
the format string. (For a complete list of symbols, see the documentation at
www.php.net.) The parts of the date can be separated by hyphens (-), dots
(.), slashes (/), or spaces.
Table 5-4 Date Format Symbols
Symbol Meaning Example
M Month in text, abbreviated Jan
F Month in text not abbreviated January
m Month in numbers with leading zeros 02 or 12
n Month in numbers without leading zeros 1 or 12
d Day of the month; two digits with leading zeros 01 or 14
j Day of the month without leading zeros 3 or 30
l Day of the week in text not abbreviated Friday
D Day of the week in text as an abbreviation Fri
w Day of the week in numbers from 0 (Sunday) 5
to 6 (Saturday)
Y Year in four digits 2004
y Year in two digits 04
g Hour between 0 and 12 without leading zeros 2 or 10
G Hour between 0 and 24 without leading zeros 2 or 15
h Hour between 0 and 12 with leading zeros 01 or 10
H Hour between 0 and 12 with leading zeros 00 or 23
i Minutes 00 or 59
s Seconds 00 or 59
a am or pm in lowercase am
A AM or PM in uppercase AM
U Unix seconds 1056244941
93 Chapter 5: Working with Data
Storing a timestamp in a variable
You can assign a timestamp with the current date and time to a variable with
the following statement:
$today = time();
Another way to store a current timestamp is with the following statement:
$today = strtotime(“today”);
You can store a specific date and time as a timestamp by using the function
mktime. The format is
$importantDate = mktime(h,m,s,mo,d,y);
where h is hours, m is minutes, s is seconds, mo is month, d is day, and y is
year. For example, you would store the date January 15, 2003, by using the
following statement:
$importantDate = mktime(0,0,0,1,15,2003);
You can also store specific timestamps by using strtotime with various keywords
and abbreviations that are very much like English. For instance, you
can create a timestamp for January 15, 2003, as follows:
$importantDate = strtotime(“January 15 2003”);
strtotime recognizes the following words and abbreviations:
Month names: Twelve month names and abbreviations
Days of the week: Seven days and some abbreviations
Time units: Year, month, fortnight, week, day, hour, minute, second;
am, pm
Some useful English words: Ago, now, last, next; this, tomorrow,
yesterday
Plus and minus: + or -
All numbers
Time zones: For example, gmt (Greenwich Mean Time), pdt (Pacific
Daylight Time), and akst (Alaska Standard Time)
94 Part II: Variables and Data
You can combine the words and abbreviations in a variety of ways. The following
statements are all valid:
$importantDate = strtotime(“tomorrow”); #24 hours from now
$importantDate = strtotime(“now + 24 hours”);
$importantDate = strtotime(“last saturday”);
$importantDate = strtotime(“8pm + 3 days”);
$importantDate = strtotime(“2 weeks ago”); # at current time
$importantDate = strtotime(“next year gmt”); #1 year from now
$importantDate = strtotime(“tomorrow 4am”);
You can find differences between timestamps by using subtraction. For example,
if $importantDate is in the past and you want to know how long ago
$importantDate was, you can subtract it from the variable $today you
defined earlier. For example:
$timeSpan = $today – $importantDate;
This gives you the number of seconds between the important date and today.
You can also use the following statement to find out how many hours have
transpired since the important date:
$timeSpan =(($today – $importantDate)/60)/60;
95 Chapter 5: Working with Data
96 Part II: Variables and Data
Chapter 6
Storing Data in Groups
by Using Arrays
In This Chapter
Building arrays
Assigning values to arrays
Sorting arrays
Using values in arrays
Building multidimensional arrays
Arrays are complex variables that store a group of values under a single
variable name. An array is useful for storing a group of related values.
For example, you can store information about a car, such as model, color, and
cost, in a single array named $FordInfo. Information in an array can be handled,
accessed, and modified easily. For example, PHP has several methods
for sorting the information inside an array.
In this chapter, you find out how to create, modify, copy, and use arrays.
Creating and Working with Arrays
Arrays are an important feature in PHP programming. This section describes
how to create, modify, and remove arrays.
Creating arrays
To create a variable, you assign a value to it. Similarly, the simplest way to
create an array is to assign a value to it. For instance, assuming that you have
not referenced $customers at any earlier point in the script, the following
statement creates an array called $customers:
$customers[1] = “Sam Smith”;
At this point, the array named $customers has been created and holds only
one value — Sam Smith. Next, you use the following statements:
$customers[2] = “Sue Jones”;
$customers[3] = “Mary Huang”;
Now, the array $customers contains three values: Sam Smith, Sue Jones, and
Mary Huang.
An array can be viewed as a list of key/value pairs, stored as follows:
$arrayname[‘key1’] = value1;
$arrayname[‘key2’] = value2;
$arrayname[‘key3’] = value3;
and so on up to any number of elements in the array.
The key is also referred to as the index.
Arrays can use either numbers or strings for keys. In the $customers array,
the keys are numbers — 1, 2, and 3. However, you can also use strings for
keys. For example, the following statements create an array of state capitals:
$capitals[‘CA’] = “Sacramento”;
$capitals[‘TX’] = “Austin”;
$capitals[‘OR’] = “Salem”;
Or you can use shortcuts to create arrays, rather than write separate assignment
statements for each number. One shortcut uses the following statements:
$streets[] = “Elm St.”;
$streets[] = “Oak Dr.”;
$streets[] = “7th Ave.”;
When you create an array by using this shortcut, the values are automatically
assigned keys that are serial numbers, starting with the number 0. For example,
consider the following statement:
echo “$streets[0]”;
It sends the following output:
Elm St.
98 Part II: Variables and Data
The first value in an array with a numbered index is 0, unless you deliberately
set it to a different number. One common mistake when working with arrays
is to think of the first number as 1, rather than 0.
An even shorter shortcut is to use the following statement:
$streets = array ( “Elm St.”,”Oak Dr.”,”7th Ave.”);
This statement creates the same array as the preceding shortcut. It assigns
numbers as keys, starting with 0. If you want the array to start with the
number 12, instead of 0, you can use the following statement:
$streets = array ( 12 => “Elm St.”,”Oak Dr.”,”7th Ave.”);
This statement creates an array as follows:
$streets[12] = Elm St.
$streets[13] = Oak Dr.
$streets[14] = 7th Ave.
You can use a similar statement to create arrays with words as keys. For
example, the following statement creates the array of state capitals with an
array statement, instead of using separate statements for each element of the
array:
$capitals = array ( “CA” => “Sacramento”,
“TX” => “Austin”,
“OR” => “Salem” );
Notice the structure of this statement. PHP doesn’t pay attention to the white
spaces or new lines. The statement could be written as one long line. The
organization of this statement is solely to make it easier for people to read.
You should make your statements as clear and legible as possible. When you
are troubleshooting your scripts, you will be glad you took the time to make
them more people-friendly.
You can also create an array with a range of values by using the following
statement:
$years = range(2001, 2010);
The resulting array looks like the following:
$years[0] = 2001
$years[1] = 2002
. . .
$years[8] = 2009
$years[9] = 2010
99 Chapter 6: Storing Data in Groups by Using Arrays
Similarly, you can use a statement, as follows:
$reverse_letters = range(“z”, “a”);
This statement creates an array with 26 elements:
$reverse_letters[0]=z
$reverse_letters[1]=y
. . .
$reverse_letters[24]=b
$reverse_letters[25]=a
Viewing arrays
You can see the structure and values of any array by using one of two
statements — var_dump or print_r. The print_r() statement, however,
gives somewhat less information. To display the $customers array, use
the following statement:
print_r($customers);
This print_r statement provides the following output:
Array
(
[1] => Sam Smith
[2] => Sue Jones
[3] => Mary Huang
)
This output shows the key and the value for each element in the array. To get
more information, use the following statement:
var_dump($customers);
This statement gives the following output:
array(3) {
[1]=>
string(9) “Sam Smith”
[2]=>
string(9) “Sue Jones”
[3]=>
string(10) “Mary Huang”
}
This output shows the data type of each element, such as a string of 9 characters,
in addition to the key and value. An array containing the customer
name and age would display as follows:
100 Part II: Variables and Data
array(2) {
[“name”]=>
string(9) “Sam Smith”
[“age”]=>
int(12)
}
The integer value is identified as an integer with int, and the value of age is
shown. This customer is 12 years old.
Remember, this output is sent by PHP. If you’re using PHP for the Web, the
output displays on the Web page with HTML, which means that it displays in
one long line. To see the output on the Web in the useful format that I describe
here, send HTML tags that tell the browser to display the text as received, without
changing it, by using the following statements:
echo “<pre>”;
var_dump($customers);
echo “</pre>”;
Modifying arrays
Arrays can be changed at any time in the script, just as variables can. The
individual values can be changed, elements can be added or removed, and
elements can be rearranged. For example, if you have an existing array named
$capitals, you can use the following statement to change the value of an
element:
$capitals[‘TX’] = “Big Springs”;
This statement changes the value of this element of the $capitals array,
although the people in Austin might object to the change. Or you could use
the following statement:
$capitals[‘RI’] = “Providence”;
The statement adds a new element to the array, leaving the existing elements
intact.
Suppose that your array has numbers for keys, as is the case with the following
array, which is created at the beginning of a script:
$customers[1] = Sam Smith
$customers[2] = Sue Jones
$customers[3] = Mary Huang
101 Chapter 6: Storing Data in Groups by Using Arrays
You can use the following statement later in the script:
$customers[] = “Juan Lopez”;
$customers now becomes an array with four elements, as follows:
$customers[1] = Sam Smith
$customers[2] = Sue Jones
$customers[3] = Mary Huang
$customers[4] = Juan Lopez
You can also copy an entire existing array into a new array with this statement:
$customerCopy = $customers;
Removing values from arrays
Sometimes you need to completely remove a value from an array. For example,
suppose you have the following array:
$colors = array ( “red”, “green”, “blue”, “pink”, “yellow” );
This array has five values. Now you decide that you no longer like the color
pink, so you use the following statement to try to remove pink from the array:
$colors[3] = “”;
Although this statement sets $colors[3] to blank, it does not remove it from
the array. You still have an array with five values, one of the values being an
empty string. To totally remove the item from the array, you need to unset it
with the following statement:
unset($colors[3]);
Now your array has only four values in it and looks as follows:
$colors[0] = red
$colors[1] = green
$colors[2] = blue
$colors[4] = yellow
Notice that the other keys did not change when element 3 was removed.
After an array has been created, it does not cease to exist unless it is deliberately
removed. Removing all the values doesn’t remove the array itself, just
102 Part II: Variables and Data
like removing all the drawers from a dresser doesn’t make the dresser disappear.
To remove the array itself, you can use the following statement:
unset($colors);
Sorting Arrays
One of the most useful features of arrays is that PHP can sort them for you.
PHP originally stores array elements in the order in which you create them.
If you display the entire array without changing the order, the elements are
displayed in the order in which they were created. Often, you want to change
this order. For example, you may want to display the array in alphabetical
order by value or by key.
PHP can sort arrays in a variety of ways. To sort an array that has numbers
as keys, use a sort statement as follows:
sort($arrayname);
This statement sorts arrays by the values and assigns new keys that are the
appropriate numbers. The values are sorted with numbers first, uppercase
letters next, and lowercase letters last. For example, consider the $streets
array:
$streets[0] = “Elm St.”;
$streets[1] = “Oak Dr.”;
$streets[2] = “7th Ave.”;
You enter the following sort statement:
sort($streets);
Now the array becomes as follows:
$streets[0] = “7th Ave.”;
$streets[1] = “Elm St.”;
$streets[2] = “Oak Dr.”;
If you use sort() to sort an array with words as keys, the keys are changed
to numbers, and the word keys are thrown away.
To sort arrays that have words for keys, use the asort statement as follows:
asort($capitals);
103 Chapter 6: Storing Data in Groups by Using Arrays
This statement sorts the capitals by value, but it keeps the original key for
each value instead of assigning a number key. For example, consider the state
capitals array created in the preceding section:
$capitals[‘CA’] = “Sacramento”;
$capitals[‘TX’] = “Austin”;
$capitals[‘OR’] = “Salem”;
You use the following asort statement,
asort($capitals);
The array becomes as follows:
$capitals[‘TX’] = Austin
$capitals[‘CA’] = Sacramento
$capitals[‘OR’] = Salem
Notice that the keys stayed with the value when the elements were reordered.
Now the elements are in alphabetical order, and the correct state key is still
with the appropriate state capital. If the keys has been numbers, the numbers
would now be in a different order. For example, suppose the original array was
as follows:
$capitals[1] = “Sacramento”;
$capitals[2] = “Austin”;
$capitals[3] = “Salem”;
After an asort statement, the new array would be as follows:
$capitals[2] = Austin
$capitals[1] = Sacramento
$capitals[3] = Salem
It’s unlikely that you want to use asort on an array with numbers as a key.
You can use several other sort statements to sort in other ways. Table 6-1
lists all the available sort statements.
Table 6-1 Ways You Can Sort Arrays
Sort Statement What It Does
sort($arrayname) Sorts by value; assigns new numbers as the keys.
asort($arrayname) Sorts by value; keeps the same key.
rsort($arrayname) Sorts by value in reverse order; assigns new numbers
as the keys.
104 Part II: Variables and Data
Sort Statement What It Does
arsort($arrayname) Sorts by value in reverse order; keeps the
same key.
ksort($arrayname) Sorts by key.
krsort($arrayname) Sorts by key in reverse order.
usort($arrayname, Sorts by a function (see Chapter 8 for information
functionname) on functions).
natsort($arrayname) Sorts mixed string/number values in natural order.
For example, given an array with values day1, day5,
day11, day2, it sorts into the following order: day1,
day2, day5, day11. The previous sort functions sort
the array into this order: day1, day11, day2, day5.
Using Arrays in Statements
Arrays can be used in statements in the same way that variables are used in
statements. This section shows the use of arrays in PHP statements.
You can retrieve any individual value in an array by accessing it directly, as in
the following example:
$CAcapital = $capitals[‘CA’];
echo $CAcapital ;
You get the following output from these statements:
Sacramento
If you use an array element that doesn’t exist in a statement, a notice is displayed.
For example, suppose you use the following statement:
$CAcapital = $capitals[‘CAx’];
If the array $capitals exists, but no element has the key CAx, you see the
following notice:
Notice: Undefined index: CAx in d:\testarray.php on line 9
A notice does not cause the script to stop. Statements after the notice will
continue to execute. But because no value has been put into $CAcapital,
any subsequent echo statements will echo a blank space. You can prevent
the notice from being displayed by using the @ symbol:
105 Chapter 6: Storing Data in Groups by Using Arrays
@$CAcapital = $capitals[‘CAx’];
Using arrays in echo statements
You can echo an array value like this:
echo $capitals[‘TX’];
It displays the following:
Austin
If you include the array value in a longer echo statement that’s enclosed by
double quotes, you may need to enclose the array value name in curly braces
like this:
echo “The capital of Texas is {$capitals[‘TX’]}”;
The output is as follows:
The capital of Texas is Austin
Using arrays in list statements
You can retrieve several values at once from an array with the list statement.
The list statement copies values from an array into variables. Suppose you
create the following array:
$shoeInfo = array(“loafer”, “black”, 22.00);
You can display the array with the following statement:
print_r($shoeInfo);
The output is as follows:
Array
(
[0] => loafer
[1] => black
[2] => 22
)
106 Part II: Variables and Data
The following statements show the use of the list statement on the
$shoeInfo array:
list($first,$second) = $shoeInfo;
echo $second,” “,$first;
This list statement creates two variables named $first and $second and
copies the first two values from $shoeInfo into the two new variables, as if
you had used the following two statements:
$first=$shoeInfo[0];
$second=$shoeInfo[1];
The third value in $shoeInfo is not copied into a variable because the list
statement contains only two variables. The output from the echo statement
is as follows:
black loafer
In some cases, you may want to retrieve the key from an array element rather
than the value. Suppose the following element is the first element in an array:
$shoeInfo[‘style’] = loafer;
The following statements retrieve the key, along with the value, and echo
them:
$value = $shoeInfo[‘style’];
$key = key($shoeInfo);
echo “$key: $value”;
The output from these statements is as follows:
style: loafer
The first statement puts loafer into $value. The second statement puts
style into $key. The key statement gets the key of an array element. In this
case, it retrieves the key from the first element because that was the current
element where the pointer is located. You can get any key in the array by
walking through the array. The next section explains what the pointer is and
how to walk through arrays.
Walking through an Array
You will often want to do something to every value in an array. You may want
to echo each value, store each value in a database, or add six to each value in
107 Chapter 6: Storing Data in Groups by Using Arrays
the array. In technical talk, walking through each and every element in an
array, in order, is called iteration. It is also sometimes called traversing. This
section describes two ways to walk through an array:
Traversing an array manually: Uses a pointer to move from one array
value to another
Using foreach: Automatically walks through the array, from beginning
to end, one value at a time
Traversing an array manually
You can walk through an array manually by using a pointer. To do this, think of
your array as a list. Imagine a pointer pointing to a value in the list. The pointer
stays on a value until you move it. After you move it, it stays there until you
move it again. You can move the pointer with the following instructions:
current($arrayname): Refers to the value currently under the pointer;
does not move the pointer
next($arrayname): Moves the pointer to the value after the current value
previous($arrayname): Moves the pointer to the value before the current
pointer location
end($arrayname): Moves the pointer to the last value in the array
reset($arrayname): Moves the pointer to the first value in the array
The following statements manually walk through an array containing state
capitals:
$value = current ($capitals);
echo “$value<br>”;
$value = next ($capitals);
echo “$value<br>”;
$value = next ($capitals);
echo “$value<br>”;
Unless you have moved the pointer previously, the pointer is located at the
first element when you start walking through the array. If you think the array
pointer may have been moved earlier in the script or if your output from the
array seems to start somewhere in the middle, use the reset statement
before you start walking, as follows:
reset($capitals);
Using this method to walk through an array, you need an assignment statement
and an echo statement for every value in the array — for each of the 50
states. The output is a list of all the state capitals.
108 Part II: Variables and Data
This method gives you flexibility. You can move through the array in any
manner, not just one value at a time. You can move backwards, go directly
to the end, skip every other value by using two consecutive next statements,
or employ whatever method is useful. However, if you want to go through the
array from beginning to end, one value at a time, PHP provides an easier
method: the foreach statement, which does exactly what you need more
efficiently. The foreach statement is described in the next section.
Using foreach to walk through an array
You can use foreach to walk through an array one value at a time and execute
a block of statements by using each value in the array. The general
format is as follows:
foreach ( $arrayname as $keyname => $valuename )
{
block of statements;
}
In this format, you need to fill in the following information:
arrayname: The name of the array you are walking through.
keyname: The name of the variable where you want to store the key. The
keyname variable is optional. If you leave out $keyname =>, only the
value is stored into $valuename.
valuename: The name of the variable where you want to store the value.
For example, the following foreach statement walks through a sample array
of state populations and echoes a list:
$state_population = array ( “CA” => 34501130,
“WY” => 494423,
“OR” => 3472867);
ksort($state_population);
foreach($state_population as $state => $population )
{
$population = number_format($population);
echo “$state: $population.<br>”;
}
The preceding statements give the following Web page output:
CA: 34,501,130
OR: 3,472,867
WY: 494,423
109 Chapter 6: Storing Data in Groups by Using Arrays
You can use the following line in place of the foreach line in the previous
statements:
foreach ( $state_population as $population )
With this statement, the key (state) is not stored in a variable. Only the populations
are available for the output.
When foreach starts walking through an array, it moves the pointer to the
beginning of the array. You don’t need to reset an array before walking
through it with foreach.
Finding Array Size
To see the structure and values of your array, you can use var_dump and
print_r (described earlier in this chapter in “Viewing arrays”), but sometimes
you just want to know the size of your array, rather than see everything
that’s in it.
You can find out the size of your array by using either the count statement or
a sizeof statement. The format for these statements is as follows:
$n = count($arrayname);
$n = sizeof($arrayname);
After either of these statements, $n will contain the number of elements in
the array.
Converting Arrays into Strings
(And Vice Versa)
Sometimes you want to perform an operation on information, but the operation
requires the information to be in a different format. For instance, you may
want to display every word in a sentence on a separate line. One way to do this
is to add a \n on the end of each word before you display it. You could use a
foreach statement to do that easily if the sentence is in an array, rather than
in a string. PHP allows you to create an array that contains one word of the sentence
in each element.
You can create an array that contains the contents of a string by using a
statement in the following format:
$arrayname = explode(“s”,string);
110 Part II: Variables and Data
The first item in the parentheses (s) is the character to use to divide the
string. The second item is the string itself. For example, the following statement
creates an array that contains the characters in a string:
$string1 = “This:is a: new:house”;
$testarray = explode(“:”,$string1);
print_r($testarray);
The explode statement tells PHP to split the string at each colon (:) and
create an array containing the substrings. The output is the following:
Array
(
[0] => This
[1] => is a
[2] => new
[3] => house
)
$string1 is not affected.
Conversely, you can convert an array into a string by using the following
statement:
$resString = implode(“s”,$array);
The statement tells PHP to create a string containing all the elements in
$array, with s separating the text from each array element, and store the
string in $resString. For example, you could use the following statements:
$arrayIn = array( “red”, “blue”, “green”);
$stringOut = implode(“;”,$arrayIn);
echo $stringOut;
The output string from implode is stored in $stringOut. The implode
statement, as you might guess, doesn’t affect $arrayIn. In general, these
statements do not affect the input to the statement; they just read it. If
any statement changes the input, I will point it out to you.
The following is the output of this echo statement:
red;blue;green
There is no space between the elements in the string because no space was
specified in the implode statement. Using a space in s, as in the following
implode statement, puts spaces into the resulting string:
$stringOut = implode(“; “,$arrayIn);
111 Chapter 6: Storing Data in Groups by Using Arrays
With this statement, the output is as follows:
red; blue; green
Converting Variables into
Arrays (And Vice Versa)
Sometimes you want the information in an array stored in variables that you
can use in PHP statements. Or you need variables converted to array elements.
For example, you might want to perform the same operation on a
bunch of variables, such as add 1 to each variable value. If you convert the
variables into elements of an array, you can use one foreach statement to
access the variable values one at a time, rather than write a bunch of statements
to access each variable separately.
Using the extract statement, you can retrieve all the values from an array,
and insert each value into a variable, by using the key for the variable name.
In other words, each array value is copied into a variable named for the key.
For example, the following statements get all the information from an array
and echo it:
$testarray = array( “pink”=>”carnation”, “red”=>”rose”);
extract($testarray);
echo “My favorite red flower is a $red.\n”;
echo “My favorite pink flower is a $pink.”;
The output for these statements is the following:
My favorite red flower is a rose.
My favorite pink flower is a carnation.
Conversely, you can also convert a group of simple variables into an array by
using a compact statement that copies the value from each specified variable
name into an array element. The use of the compact statement is, shown in
the following statements:
$color1 = “red”;
$color2 = “blue”;
$a = “purple”;
$b = “orange”;
$arrayIn = array(“a”,”b”);
$arrayOut = compact(“color1”,”color2”,$arrayIn);
112 Part II: Variables and Data
The result is the following array:
$arrayOut[color1] = red
$arrayOut[color2] = blue
$arrayOut[a] = purple
$arrayOut[b] = orange
As you can see, the names of the variables are used as the keys.
Notice that two different methods are used in the compact statement to specify
the variables that make up the array:
First method: You can use the variable names directly, as strings. The
two variables color1 and color2 in the example show this method.
Second method: You use an array that contains the names of the variables.
In the previous code, $arrayIn contains the variable names: a
and b. Then in the compact statement, the array name is used to add the
variables to the array.
You can use either method. If you have only a few variables to compact into
an array, the first method of just using the variable names is probably fine.
However, if you have a lot of variables to include, you may prefer putting the
names into an array first, and then using the array in the compact statement.
Splitting and Merging Arrays
You often need to put arrays together or take them apart. For example, suppose
you have two classes of students and you have two arrays, each of which stores
the names of the students in one class. If the two classes were to merge, you
would want to merge the two arrays containing the student names.
You can split an array by creating a new array that contains a subset of an
existing array. You can do this by using a statement of the following general
format:
$subArray = array_slice($arrayname,n1,n2);
The n1 in the statement is the sequence number of the element where the
new array should start, such as 0 for the first element in the array or 1 for the
second element. The n2 is the length of the new array. For example, consider
the following statements:
$testarray = array( “red”, “green”, “blue”,”pink”);
$subArray = array_slice($testarray,1,2);
113 Chapter 6: Storing Data in Groups by Using Arrays
The new array, $subArray, will contain the following:
[0] => green
[1] => blue
It starts with element 1 of $testarray and takes 2 elements.
Unless you specify otherwise, arrays begin with 0, not 1. Therefore, element 1
of $testarray is green. Red is element 0.
Conversely, you can merge two or more arrays together by using the following
statement:
$bigArray = array_merge($array1,$array2,…);
For example, you might use the following statements to merge arrays:
$array1 = array(“red”,”blue”);
$array2 = array(“green”,”yellow”);
$bigArray = array_merge($array1,$array2);
After the statement, $bigArray is the following array:
$bigArray[0] = red
$bigArray[1] = blue
$bigArray[2] = green
$bigArray[3] = yellow
You can merge arrays with keys that are words, rather than numbers, as well.
However, if the keys are the same for any of the elements, the later element
with the same key word will overwrite the first element of the same key. For
example, suppose you merge the following arrays:
$array1 = array(“color1”=>”red”,”color2”=>”blue”);
$array2 = array(“color1”=>”green”,”color3”=>”yellow”);
$bigArray = array_merge($array1,$array2);
The output array is as follows:
$bigArray[color1] = green
$bigArray[color2] = blue
$bigArray[color3] = yellow
If you need to merge arrays that have identical keys, you can use the statement
array_merge_recursive rather than array_merge. The array_merge_
recursive statement creates a multidimensional array when keys are identical,
instead of overwriting the value as array_merge does. Multidimensional arrays
are explained in the section, “Multidimensional Arrays,” later in this chapter.
114 Part II: Variables and Data
Comparing Arrays
You may need to know whether two arrays are the same. You can identify
the elements that are different or the elements that are the same. To find
out which elements are different, use the following statement:
$diffArray = array_diff($array1,$array2,…);
After this statement, $diffArray contains the elements from $array1 that are
not present in any of the other listed arrays. The elements in the result array
will have the same keys. For example, you can use the following statements:
$array1 = array( “a”=>”apple”, “b”=>”orange”, “c”=>”banana”);
$array2 = array( “prune”, “orange”, “banana” );
$diffArray = array_diff($array1,$array2);
After this code, $diffArray looks like this:
$diffArray[a] = apple;
The element apple is in the array because apple is in $array1 but not in
$array2.
The order in which you list the arrays to be compared makes a difference.
For example, if you used the following statement, instead of the preceding
one, you’d get a different output:
$diffArray = array_diff($array2,$array1);
After this statement, $diffArray looks like the following:
$diffArray[0] = prune;
Because $array2 is listed first in this statement, the resulting difference
array contains only prune because prune is in $array2, listed first, but not
in $array1, listed second.
If you want to find array elements that differ in either the value or the key,
you can use the following statement:
$diffArray = array_diff_assoc($array1,$array2);
Using the same $array1 and $array2 as the previous examples, the resulting
array would look like this:
$diffArray[a] = apple
$diffArray[b] = orange
$diffArray[c] = banana
115 Chapter 6: Storing Data in Groups by Using Arrays
In this case, none of the elements in $array1 appear in $array2 because the
keys are all different.
You can create an array that contains the elements that are the same, rather
than different, in two or more arrays by using the following statement:
$simArray = array_intersect($array1,$array2,. . .);
For example, using the same arrays, you could use the following statement:
$simArray = array_intersect($array1,$array2);
The results array would look like this:
$simArray[b] = orange
$simArray[c] = banana
This array_intersect statement adds an element to the new array for any
values that are in both the arrays. If you want both the value and the key to
be the same, use the following statement:
$simArray = array_intersect_assoc($array1,$array2);
This statement requires both the value and the key to be identical before
adding an element to the array. Using the same arrays, $simArray is empty
after the statement, because even though two of the values are the same,
none of the keys are the same.
Working with Other Array Operations
The following sections describe these miscellaneous operations on arrays:
Adding the values of an array
Removing duplicate items from an array
Exchanging keys and values in an array
Summing arrays
To add all the values in an array, use the following statement:
$sum = array_sum($array);
116 Part II: Variables and Data
For example, you can use the following statements;
$arrayAdd = array(3,3,3);
$sum = array_sum($arrayAdd);
echo $sum;
The output is 9.
Of course, you are only going to add elements in an array of numbers. As
mentioned in Chapter 5, PHP converts strings to 0 if you try to add them.
Removing duplicate items
You sometimes need to remove duplicate elements from an array. For example,
if you want to print a list of customer names from the elements of an
array, you probably want each name listed only once. You can do so with the
following statements:
$names = array( “Mary”, “Sally”, “Sally”,”Sam”);
$names2 = array_unique($names);
The array $names2 looks like this:
$names2[0] => Mary
$names2[1] => Sally
$names2[3] => Sam
As you can see, the duplicate element and its key are not in the resulting
array.
Exchanging keys and values
You can exchange values and keys in an array. For example, suppose you
have the following array:
$testarray[‘rose’] = red
$testarray[‘iris’] = purple
To exchange the values, use the following statement:
$arrayFlipped = array_flip($testarray);
The array $arrayFlipped looks like this:
$testarray[‘red’] = rose
$testarray[‘purple’] = iris
117 Chapter 6: Storing Data in Groups by Using Arrays
Multidimensional Arrays
In the earlier sections of this chapter, I describe arrays that are a single list of
key/value pairs. However, on some occasions, you may want to store values
with more than one key. For example, suppose you want to store the following
food prices together in one variable:
onion, 0.50
apple, 2.50
orange, 2.00
bacon, 3.50
potato, 1.00
ham, 5.00
You can store these products in an array as follows:
$foodPrices[‘onion’] = 0.50;
$foodPrices[‘apple’] = 2.50;
$foodPrices[‘orange’] = 2.00;
$foodPrices[‘bacon’] = 3.50;
$foodPrices[‘potato’] = 1.00;
$foodPrices[‘ham’] = 5.00;
Your script can easily look through this array whenever it needs to know the
price of an item. But suppose you have 3,000 products. Your script would need
to look through 3,000 products to find the one with onion or ham as the key.
Notice that the list of foods and prices includes a variety of food that can be
classified into three groups: vegetable, fruit, and meat. If you classify the products,
then the script needs to look through only one classification to find the
correct price. Classifying the products is much more efficient. You can classify
the products by putting the costs in a multidimensional array as follows:
$foodPrices[‘vegetable’][‘onion’] = 0.50;
$foodPrices[‘vegetable’][‘potato’] = 1.00;
$foodPrices[‘fruit’][‘apple’] = 2.50;
$foodPrices[‘fruit’][‘orange’] = 2.00;
$foodPrices[‘meat’][‘bacon’] = 3.50;
$foodPrices[‘meat’][‘ham’] = 5.00;
This kind of array is called a multidimensional array because it’s like an array
of arrays. Figure 6-1 shows the structure of $foodPrices as an array of arrays.
The figure shows that $foodPrices has three key/value pairs. The value for
each key — vegetable, fruit, and meat — is an array with two key/value pairs.
For example, the value for the key meat is an array with the two key/value
pairs: bacon/3.50 and ham/5.00.
118 Part II: Variables and Data
$foodPrices is a two-dimensional array. PHP can also understand multidimensional
arrays that are four, five, six, or more levels deep. However, my
head starts to hurt if I try to comprehend an array that is more than three
levels deep. The possibility of confusion increases as the number of dimensions
increases.
Creating multidimensional arrays
You can create multidimensional arrays in the same ways you create onedimensional
arrays. You can create them with a series of direct statements,
as follows:
$foodPrices[‘vegetable’][‘potato’] = 1.00;
$foodPrices[‘fruit’][‘apple’] = 2.50;
You can also use a shortcut and allow PHP to choose the keys, as follows:
transportation[‘car’][] = “Ford”;
transportation[‘car’][] = “Jeep”;
PHP will assign numbers as keys so that the array looks like the following:
transportation[car][0] = Ford;
transportation[car][1] = Jeep;
You can also create a multidimensional array by using the array statement, as
follows:
$foodPrices = array(
“vegetable”=>array(“potato”=>1.00,”onion”=>.50),
“fruit”=>array(“apple”=>2.50,”orange”=>2.00));
Notice that foodPrices is an array, created by the first array statement. The
first array statement sets two elements — vegetable and fruit. The values for
the two elements are themselves set by array statements, resulting in an array
of arrays. This statement creates the following multidimensional array:
$foodPrices key value
key value
vegetable onion 0.50
potato 1.00
fruit orange 2.00
apple 2.50
meat bacon 3.50
ham 5.00
Figure 6-1:
The
structure of
$food
Prices, an
array of
arrays.
119 Chapter 6: Storing Data in Groups by Using Arrays
$foodPrices[vegetable][potato] = 1.00
$foodPrices[vegetable][onion] = .50
$foodPrices[fruit][apple] = 2.50
$foodPrices[fruit][orange] = 2.00
Viewing multidimensional arrays
You can view a multidimensional array in the same ways you can view any
array — by using the print_r or the var_dump statements. The output of
the var_dump statement is shown here:
array(2) {
[“vegetable”]=>
array(2) {
[“potato”]=>
float(1)
[“onion”]=>
float(0.5)
}
[“fruit”]=>
array(2) {
[“apple”]=>
float(2.5)
[“orange”]=>
float(2)
}
}
The first line identifies the first array and says it has two elements. The first
element, with the key vegetable, contains an array of two elements with the
keys potato with a value of 1 of type float, and the second element with the
key onion and a value of 0.5 of type float. The second element of the main
array, with the key fruit, also contains an array with two elements.
Using multidimensional
arrays in statements
You can get values from a multidimensional array by using the same procedures
that you use with a one-dimensional array. For example, you can
access a value directly with this statement:
$hamPrice = $foodPrices[‘meat’][‘ham’];
You can also echo the value:
echo $foodPrices[‘meat’][‘ham’];
120 Part II: Variables and Data
However, if you combine the value within double quotes, you need to use
curly braces to enclose the variable name. The $ that begins the variable
name must follow the { immediately, without a space, as follows:
echo “The price of ham is \${$foodPrices[‘meat’][‘ham’]}”;
Notice the backslash (\) in front of the first dollar sign ($). The backslash
tells PHP that $ is a literal dollar sign, not the beginning of a variable name.
The output is
The price of ham is $5
Earlier in this chapter, I describe several statements that convert strings to
arrays (and vice versa) and convert arrays to variables (and vice versa) and
statements for other operations on arrays. Most of the statements don’t
make sense with multidimensional arrays and won’t work correctly. However,
remember that a multidimensional array is an array of arrays. Therefore, you
can use one of the elements of the multidimensional array (which is an array
itself) in these statements. For instance, the implode statement described earlier
in this chapter converts an array into a string. You can’t use the implode
statement with a multidimensional array because its values are arrays, not
strings. However, you can use any one of the elements in the implode statements,
as follows:
$resString = implode(“: “,$foodPrices[‘vegetable’]);
This statement puts the value for each element of the vegetable array into
the string, separating them by :. When you echo $resString, you see the
following output:
1: 0.5
The output is the value of potato (1) and the value of onion (0.5). The two
values are separated by a semicolon and a space, as specified in the implode
statement.
Walking through a multidimensional array
You can walk through a multidimensional array by using foreach statements
(described in the section “Walking through an Array,” earlier in this chapter).
Because a two-dimensional array, such as $foodPrices, contains two arrays,
it takes two foreach statements to walk through it. One foreach statement
is inside the other foreach statement. (Putting statements inside other statements
is called nesting.)
121 Chapter 6: Storing Data in Groups by Using Arrays
The following statements echo the values from the multidimensional array:
foreach ( $foodPrices as $category )
{
foreach ( $category as $food => $price )
{
$f_price = sprintf(“%01.2f”, $price);
echo “$food: \$$f_price \n”;
}
}
The output is the following:
onion: $0.50
potato: $1.00
apple: $2.50
orange: $2.00
bacon: $3.50
ham: $5.00
Here is how PHP interprets these foreach statements:
1. The first key/value pair in the $foodPrices array is retrieved, and the
value is stored in the variable $category. (The value is an array.)
2. The first key/value pair in the $category array is retrieved. The key is
stored in $food, and the value is stored in $price.
3. The value in $price is formatted into the correct format for money.
4. One row for the product and its price is echoed.
5. The next key/value pair in the $category array is reached.
6. The price is formatted, and the next row for the food and its price is
echoed.
7. Because there are no more key/value pairs in $category, the inner
foreach statement ends.
8. The next key/value pair in the outer foreach statement is reached. The
next value is put in $category, which is an array.
9. The procedure in Steps 1 through 8 is repeated until the last key/value
pair in the last $category array is reached. The inner foreach statement
ends. The outer foreach statement ends.
In other words, the outer foreach starts with the first key/value pair in the
array. The key is vegetable, and the value of this pair is an array that is put
into the variable $category. The inner foreach then walks through the
array in $category. When it reaches the last key/value pair in $category, it
ends. The script is then back in the outer loop, which goes on to the second
key/value pair . . . and so on until the outer foreach reaches the end of the
array.
122 Part II: Variables and Data
Built-in PHP Arrays
PHP has several built-in arrays that you can use when writing PHP scripts.
Different types of information are stored in different arrays. For example,
information about your server (such as headers, paths, and script locations)
is stored in an array called $_SERVER. When you want to display the name of
the current script that is running, it’s available in the $_SERVER built-in array
in $_SERVER[‘PHP_SELF’].
Using superglobal arrays
Currently, two sets of built-in arrays contain the same information. One set of
arrays, introduced in PHP 4.1.0, are called superglobals or autoglobals because
they can be used anywhere, even inside a function. (Functions and the use of
variables inside functions are explained in Chapter 8.) The older arrays, with
long names such as $HTTP_SERVER_VARS, must be made global before they
can be used in an array, as explained in Chapter 8. Unless you’re using an old
version of PHP, use the newer arrays, those whose names begin with an
underscore (_). The older arrays should be used only when you’re forced to
use a version of PHP older than PHP 4.1.0.
A new php.ini setting introduced in PHP 5 allows you to prevent PHP from
automatically creating the older, long arrays. It’s very unlikely that you will
need to use them, unless you’re using some old scripts containing the long
variables. The following line in php.ini controls this setting:
register_long_arrays = On
At the current time, this setting is On by default. Unless you’re running old
scripts that need the old arrays, you should change the setting to Off so that
PHP doesn’t do this extra work.
Although the setting is currently On by default, that could change. The default
setting might change to Off in a future version. If you’re using some old scripts
and getting errors on lines containing the long arrays, such as $HTTP_GET_
VARS, check your php.ini setting for long arrays. It might be Off, and the long
arrays needed by the older script are not being created at all.
The built-in arrays are listed in Table 6-2, along with a short description. The
use of specific arrays is described in detail in this book where the related
subjects are described. For example, the built-in arrays that contain form
variables are discussed in Chapter 10 when I discuss the use of forms.
123 Chapter 6: Storing Data in Groups by Using Arrays
Table 6-2 Handy Built-in Arrays
Array Description
$GLOBALS Contains all the global variables. For example, if
you use the statement, $testvar = 1, you can
then access the variable as $GLOBALS
[‘testvar’].
$ _POST Contains all the variables contained in a form if
the form uses method=”post”.
$HTTP_POST_VARS Same as $ _POST.
$ _GET Contains all the variables passed from a previous
page as part of the URL. This includes variables
passed in a form using method=”get”.
$HTTP_GET_VARS Same as $ _GET.
$ _COOKIE Contains all the cookie variables.
$HTTP_COOKIE_VARS Same as $ _COOKIE.
$ _SESSION Contains all the session variables.
$HTTP_SESSION_VARS Same as $ _SESSION.
$_REQUEST Contains all the variables together that are in
$_POST, $_GET, and $_SESSION.
$_FILES Contains the names of files that have been
uploaded.
$HTTP_FILES_VARS Same as $_FILES.
$_SERVER Contains information about your server. Because
your Web server provides the information, the
information that’s available depends on what
server you’re using.
$HTTP_SERVER_VARS Same as $_SERVER.
$_ENV Contains information provided by your operating
system, such as the operating system name, the
system drive, and the path to your temp directory.
This info varies depending on your operating
system.
$HTTP_ENV_VARS Same as $_ENV.
124 Part II: Variables and Data
Using $_SERVER and $_ENV
The $_SERVER and $_ENV arrays contain different information, depending on
the server and operating system you’re using. You can see what information
is in the arrays for your particular server and operating system by using the
following statements:
foreach($_SERVER as $key =>$value)
{
echo “Key=$key, Value=$value\n”;
}
The output includes such lines as the following:
Key=DOCUMENT_ROOT, Value=c:/program files/apache
group/apache/htdocs
Key=PHP_SELF, Value=/test.php
The DOCUMENT_ROOT element shows the path to the directory where Apache
expects to find the Web page files.
The PHP_SELF element shows the file that contains the script that is currently
running.
You can see the information in the $_ENV array by using the phpinfo() statement
with a 16 to specify the environmental variables, as follows:
phpinfo(16);
Built-in arrays are available only if track-vars is enabled. As of PHP 4.0.3,
track-vars is always enabled, unless the PHP administrator deliberately
turns track-vars off when installing PHP. It’s rare that track-vars would
be turned off. If the built-in arrays don’t seem to be available, check with
phpinfo() to make sure that track-vars is turned on. If it’s turned off, PHP
has to be reinstalled.
Using $argv and $argc
Sometimes you want to pass information into a script from the outside. One
way to do this is to pass the information to the script on the command line
when you start the script. You rarely want to do this when using PHP for the
Web, but you may want to do this when running PHP CLI from the command
line. For example, suppose you write a script that can add any two numbers
125 Chapter 6: Storing Data in Groups by Using Arrays
together and you want to pass the two numbers into the script when you
start it. You can give PHP the two numbers you want it to add together when
you start the script, on the command line, as follows:
php add.php 2 3
In this statement, the script is named add.php, and 2 and 3 are the numbers
you want the script to add together. These numbers are available inside the
script in an array called $argv. This array contains all the information on the
command line, as follows:
$argv[0]=add.php
$argv[1]=2
$argv[2]=3
So, $argv always contains at least one element — the script name.
Then, in your script, you can use the following statements:
$sum = $argv[1] + $argv[2];
echo $sum;
The output is the following:
5
Another variable is also available called $argc. This variable stores the number
of elements in $argv. Thus, $argc always equals at least 1, which is the name
of the script. In the preceding example, $argc equals 3.
126 Part II: Variables and Data
Part III
Basic PHP
Programming
In this part . . .
In this part, you find out how to write complete PHP
scripts. You discover how to combine simple statements
into a finished script. You find out about complex
statements that allow you to write scripts that perform
complex tasks. You see the usefulness of reusing code and
find out how to write code that can be reused. When you
finish this part, you will know everything you need to
know to write useful and complex PHP scripts.
Chapter 7
Controlling the Flow of the Script
In This Chapter
Changing the order in which statements are executed
Setting up conditions
Joining simple conditions to make complex conditions
Using conditions in conditional statements and loops
Writing if statements
Building and using loops for repeated statements
Breaking out of loops
PHP scripts are a series of instructions in a file. PHP begins at the top
of the file and executes each instruction, in order, as it comes to it.
However, some scripts need to be more complicated. You may want your
script to display one page to new customers and a different page to existing
customers. Or you may need to display a list of phone numbers by executing
a single echo statement repeatedly, once for each phone number. This chapter
describes how to change the order in which simple statements are executed
by using complex statements such as conditional statements or loops.
Changing the Order of
Statement Execution
Simple statements in PHP are executed one after another from the beginning
of the script to the end. For example, the following statements in a script are
executed in order:
$a = “Good Morning”;
echo $a;
$a = “Good Afternoon”;
echo $a;
To change the order of execution of these statements, you have to change the
order of the statements themselves, as follows:
130 Part III: Basic PHP Programming
$a = “Good Afternoon”;
echo $a;
$a = “Good Morning”;
echo $a;
However, suppose you want to display the appropriate greeting for the time
of day. You want to echo Good Morning if it’s before noon, and you want to
echo Good Afternoon if it’s after noon. In other words, you want to do the
following:
if (time is before noon)
{
$a = Good Morning;
echo $a;
}
or else if (time is after noon)
{
$a = Good Afternoon;
echo $a;
}
To display the appropriate greeting, you need a complex statement that tests
the condition of time. PHP provides two types of complex statements that
enable you to perform tasks like this — tasks that change the order in which
statements are executed:
Conditional statements: Sometimes you need to set up statements that
execute only when certain conditions are met. For example, you may
want to provide your catalog only to customers who have paid their bills
and not to customers who owe you money. This type of statement is
called a conditional statement. The PHP conditional statements are the
if statement and the switch statement.
Looping statements: Frequently you need to set up a block of statements
that is repeated. For example, you may want to send an e-mail message to
all your customers. To do that, you can use two statements: one that gets
the customer’s e-mail address from the database and one that sends the
customer an e-mail message. You would need to repeat these two statements
for every customer in the database. The feature that enables you
to execute statements repeatedly is called a loop. Three types of loops
are for loops, while loops, and do..while loops.
Both types of complex statements execute a block of statements based on a
condition. That is, if a condition is true, the block of statements executes. In
conditional statements, the block of statements executes once. For example,
if the time is after noon, the script echoes Good Afternoon. In loops, the block
of statements executes repeatedly, until the condition is no longer true. For
example, if another customer in the database has not yet received an e-mail
message, send that person one. The loop repeats this process as long as there
is another customer who has not received an e-mail.
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Setting Up Conditions
Conditions are expressions that PHP tests or evaluates to see whether they
are true or false. Conditions are used in complex statements to determine
whether or not a block of simple statements should be executed. To set up
conditions, you compare values. Some questions you may ask in comparing
values for conditions are as follows:
Are two values equal? Is Sally’s last name the same as Bobby’s last
name? Or, is Nick 15 years old? (Does Nick’s age equal 15?)
Is one value larger or smaller than another? Is Nick younger than
Bobby? Or, did Sally’s house cost more than a million dollars?
Does a string match a pattern? Does Bobby’s name begin with an S?
Does the zip code have five numeric characters?
You can also set up conditions in which you ask two or more questions. For
example, you may ask: Is Nick older than Bobby and is Nick younger than
Sally? Or you may ask: Is today Sunday and is today sunny? Or you may ask:
Is today Sunday or is today Monday?
Using comparison operators
PHP offers several comparison operators that you can use to compare
values. Table 7-1 shows these comparison operators.
Table 7-1 Comparison Operators
Operator What It Means
== Are the two values equal in value?
=== Are the two values equal in both value and data type?
> Is the first value larger than the second value?
>= Is the first value larger than or equal to the second value?
< Is the first value smaller than the second value?
<= Is the first value smaller than or equal to the second value?
!=, <> Are the two values not equal to each other in value?
!== Are the two values not equal to each other in either value or
data type?
132 Part III: Basic PHP Programming
You can compare both numbers and strings. Strings are compared alphabetically,
with all uppercase characters coming before any lowercase characters.
For example, SS comes before Sa. Punctuation characters also have an order,
and one character can be found to be larger than another character. However,
comparing a comma to a period doesn’t have much practical value.
Strings are compared based on their ASCII code. In the ASCII character set,
each character is assigned an ASCII code that corresponds to a number
between 0 and 127. When strings are compared, they are compared based
on this code. For example, the number that represents the comma is 44. The
period corresponds to 46. Therefore, if a period and a comma are compared,
the period is seen as larger.
The following are some valid comparisons that PHP can test to determine
whether they are true:
$a == $b
$age != 21
$ageNick < $ageBobby
$house_price >= 1000000
The comparison operator that asks whether two values are equal consists
of two equal signs (==). One of the most common mistakes is to use a single
equal sign for a comparison. A single equal sign puts the value into the variable.
Thus, a statement like if ($weather = “raining”) would set
$weather to raining rather than check whether it already equaled raining,
and would always be true.
PHP tests comparisons by evaluating them and returning a Boolean value,
either TRUE or FALSE. For example, look at the following comparison:
$a == $b
If $a=1 and $b=1, the comparison returns TRUE. If $a =1 and $b =2, the comparison
returns FALSE.
If you write a negative (by using !), the negative condition is true. Look at the
following comparison:
$age != 21
The condition is that $age does not equal 21. That’s the condition that is
being tested. Therefore, if $age = 20, the comparison is TRUE.
133 Chapter 7: Controlling the Flow of the Script
Checking variable content
Sometimes you just need to know whether a variable exists or what type of
data is in the variable. Here are some common ways to test variables:
isset($varname) # True if variable is set, even if
nothing is stored in it.
empty($varname) # True if value is 0 or is a string with
no characters in it or is not set.
You can also test what type of data is in the variable. For example, to see if
the value is an integer, you can use the following:
is_int($number)
The comparison is TRUE if the value in $number is an integer. Some other
tests provided by PHP are as follows:
is_array($var2): Checks to see if $var2 is an array
is_float($number): Checks to see if $number is a floating point
number
is_null($var1): Checks to see if $var1 is equal to 0
is_numeric($string): Checks to see if $string is a numeric string
is_string($string): Checks to see if $string is a string
You can test for a negative, as well, by using an exclamation point (!) in front
of the expression. For example, the following statement returns TRUE if the
variable does not exist at all:
!isset($varname)
Pattern matching with regular expressions
Sometimes you need to compare character strings to see whether they fit
certain characteristics, rather than to see whether they match exact values.
For example, you may want to identify strings that begin with S or strings
that have numbers in them. For this type of comparison, you compare the
string to a pattern. These patterns are called regular expressions.
You have probably used some form of pattern matching in the past. When you
use an asterisk (*) as a wild card when searching for files (dir ex*.doc or
ls ex*.txt, for example), you’re pattern matching. For example, ex*.txt is
a pattern. Any string that begins with ex and ends with the string .txt, with
any characters in between the ex and the .txt, matches the pattern. The
strings exam.txt, ex33.txt, and ex3×4.txt all match the pattern. Using
regular expressions is just a more complicated variation of using wild cards.
One common use for pattern matching is to check the input from a Web page
form. If the information input doesn’t match a specific pattern, it may not be
something you want to store in your database. For example, if the user types
a zip code into your form, you know the format needs to be five numbers or
a zip + 4. So, you can check the input to see if it fits the pattern. If it doesn’t,
you know it’s not a valid zip code, and you can ask the user to type in the correct
information.
Using special characters in patterns
Patterns consist of literal characters and special characters. Literal characters
are normal characters, with no special meaning. An e is an e, for example,
with no meaning other than that it’s one of 26 letters in the alphabet.
Special characters, on the other hand, have special meaning in the pattern,
such as the asterisk (*) when used as a wild card. Table 7-2 shows the special
characters that you can use in patterns.
Table 7-2 Special Characters Used in Patterns
Character Meaning Example Matches Does Not
Match
^ Beginning ^e exam math exam
of line
$ End of line m$ exam exams
. Any single .. up, do A, 2
character Longer words
match because
they contain a
string of two
characters.
? The preceding ger?m germ, gem geam
character is
optional
( ) Groups literal g(er)m germ Gem,
characters into grem
a string that
must be
matched exactly
[ ] Encloses a set g[er]m gem, grm germ, gel
of optional literal
characters
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135 Chapter 7: Controlling the Flow of the Script
Character Meaning Example Matches Does Not
Match
[^] Encloses a set g[^er]m gym, gum gem, grem,
of nonmatching germ
optional characters
- Represents all the g[a-c]m gam, gbm, gcm gdm, gxm,
characters between gal
two characters (a
range of possible
characters)
+ One or more of the bldg bldg111, bldg,
preceding items [1-3]+ bldg132 bldg555
* Zero or more of the ge*m gm, geeem germ, grm
preceding items
{n} Repeat n times ge{5}m geeeeem geeeem,
geeeeeem
{n1,n2} Specifies a range a{2,5} aa, aaa, aaaa, 1, a3
of repetitions of 145aaaaa
the preceding
character(s).
\ The following g\*m g*m gem, germ
character is literal
( | | ) A set of alternate (Sam| Samuel Go Sarah,
strings Sally) Sally Salmon
Considering some example patterns
Literal and special characters are combined to make patterns, sometimes long
complicated patterns. A string is compared to the pattern, and if it matches,
the comparison is true. Some example patterns follow, with a breakdown of
the pattern and some sample matching and non-matching strings:
Example 1
^[A-Za-z].*
This pattern defines strings that begin with a letter and have two parts:
^[A-Za-z] The first part of the pattern dictates that the beginning of
the string must be a letter (either uppercase or lowercase).
.* The second part of the pattern tells PHP the string of characters can
be one or more characters long.
136 Part III: Basic PHP Programming
The expression ^[A-Za-z].* matches the following strings: play it
again, Sam and I.
The expression ^[A-Za-z].* does not match the following strings: 123 and ?.
Example 2
Dear (Kim|Rikki)
This pattern defines two alternate strings and has two parts:
Dear The first part of the pattern is just literal characters.
(Kim|Rikki) The second part defines either Kim or Rikki as matching
strings.
The expression Dear (Kim|Rikki) matches the following strings: Dear Kim
and My Dear Rikki.
The expression Dear (Kim|Rikki) does not match the following strings:
Dear Bobby and Kim.
Example 3
^[0-9]{5}(\-[0-9]{4})?$
This pattern defines any zip code and has several parts:
^[0-9]{5} The first part of the pattern describes any string of five
numbers.
\- The slash indicates that the hyphen is a literal.
[0-9]{4} This part of the pattern tells PHP that the next characters
should be a string of numbers consisting of four characters.
( )? These characters group the last two parts of the pattern and make
them optional.
$ The dollar sign dictates that this string should end (no characters are
allowed after the pattern).
The expression ^[0-9]{5}(\-[0-9]{4})?$ matches the following strings:
90001 and 90002-4323.
The expression ^[0-9]{5}(\-[0-9]{4})?$ does not match the following
strings: 9001 and 12-4321.
Example 4
^.+@.+\.com$
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This pattern defines any string with @ embedded that ends in .com. In other
words, it defines an e-mail address. This expression has several parts:
^.+ The first part of the pattern describes any string of one or more
characters that precedes the @.
@ This is a literal @ (at sign). @ is not a special character and does not
need to be preceded by a \.
.+ This is any string of one or more characters.
\. The slash indicates that PHP should look for a literal dot.
com$ This defines the literal string com at the end of the string, and the
$ marks the end of the string.
The expression ^.+@.+\.com$ matches the following strings: you@your
company.com and johndoe@somedomain.com.
The expression ^.+@.+\.com$ does not match the following strings: you@
yourcompany.net, you@.com, and @you.com.
Comparing strings to patterns
You can compare a string to a pattern by using ereg. The general format is as
follows:
ereg(“pattern”,value);
For example, to check the name that a user typed in a form, compare the
name (stored in the variable $name) to a pattern as follows:
ereg(“^[A-Za-z’ -]+$”,$name)
The pattern in this statement does the following:
Uses ^ and $ to signify the beginning and end of the string. That means
that all the characters in the string must match the pattern.
Encloses all the literal characters that are allowed in the string in [ ]. No
other characters are allowed. The allowed characters are upper and
lower case letters, an apostrophe (‘), a blank space, and a hyphen (-).
You can specify a range of characters using a hyphen within the [ ]. When
you do that, as in A-Z above, the hyphen does not represent a literal character.
Since you want the hyphen included as a literal character that is
allowed in your string, you need to add a hyphen that is not between any
two other characters. In this case, the hyphen is included at the end of the
list of literal characters,
Follows the list of literal characters in the [ ] with a +. The plus sign
means that the string can contain any number of the characters inside
the [ ], but must contain at least one character.
138 Part III: Basic PHP Programming
Joining multiple comparisons
Often you need to ask more than one question to determine your condition.
For example, suppose your company offers catalogs for different products in
different languages. You need to know which type of product catalog the customer
wants to see and which language he or she needs to see it in. This
requires you to join comparisons, which have the following the general
format:
comparison1 and|or|xor comparison2 and|or|xor comparison3
and|or|xor …
Comparisons are connected by one of the following three words:
and: Both comparisons are true.
or: One of the comparisons or both of the comparisons are true.
xor: One of the comparisons is true but not both of the comparisons.
Table 7-3 shows some examples of multiple comparisons.
Table 7-3 Multiple Comparisons
Condition Is True If . . .
$ageBobby == 21 Bobby is 21 or 22 years of age.
or $ageBobby == 22
$ageSally > 29 and Sally is older than 29 and lives in Oregon.
$state ==”OR”
$ageSally > 29 Sally is older than 29 or lives in Oregon or both.
or $state == “OR”
$city == “Reno” The city is Reno or the state is Oregon, but
xor $state == “OR” not both.
$name != “Sam” The name is anything except Sam and age is
and $age < 13 under 13 years of age.
You can string together as many comparisons as necessary. The comparisons
using and are tested first, the comparisons using xor are tested next, and the
comparisons using or are tested last. For example, the following condition
includes three comparisons:
$resCity == “Reno” or $resState == “NV” and $name == “Sally”
139 Chapter 7: Controlling the Flow of the Script
If the customer’s name is Sally and she lives in NV, this statement is true. The
statement is also true if she lives in Reno, regardless of what her name is.
This condition is not true if she lives in NV but her name is not Sally. You get
these results because the script checks the condition in the following order:
1. The and is compared.
The script checks $resState to see if it equals NV and checks $name to
see if it equals Sally. If both match, the condition is true, and the script
does not need to check or. If only one or neither of the variables equal
the designated value, the testing continues.
2. The or is compared.
The script checks $resCity to see if it equals Reno. If it does, the condition
is true. If it doesn’t, the condition is false.
You can change the order in which comparisons are made by using parentheses.
The connecting word inside the parentheses is evaluated first. For example,
you can rewrite the previous statement with parentheses as follows:
($resCity == “Reno or $resState == “NV”) and $name == “Sally”
The parentheses change the order in which the conditions are checked. Now
the or is checked first because it is inside the parentheses. This condition
statement is true if the customer’s name is Sally and she lives in either Reno
or NV. You get these results because the script checks the condition as follows:
1. The or is compared.
The script checks to see if $resCity equals Reno or $resState equals
NV. If it does not, the entire condition is false, and testing stops. If it
does, this part of the condition is true. However, the comparison on the
other side of the and must also be true, so the testing continues.
2. The and is compared.
The script checks $name to see if it equals Sally. If it does, the condition
is true. If it does not, the condition is false.
Use parentheses liberally, even when you believe you know the order of the
comparisons. Unnecessary parentheses can’t hurt, but comparisons that
have unexpected results can.
If you’re familiar with other languages, such as C, you may have used || (for
or) and && (for and) in place of the words. The || and && work in PHP as well.
The statement $a < $b && $c > $b is just as valid as the statement $a <
$b and $c > $b. The || is checked before the word or, and the && is
checked before the word and.
140 Part III: Basic PHP Programming
Using Conditional Statements
A conditional statement executes a block of statements only when certain conditions
are true. Here are two useful types of conditional statements:
An if statement: Sets up a condition and tests it. If the condition is true,
a block of statements is executed.
A switch statement: Sets up a list of alternative conditions. It tests for
the true condition and executes the appropriate block of statements.
Using if statements
An if statement tests conditions, executing a block of statements when a condition
is true. The general format of an if conditional statement is as follows:
if ( condition )
{
block of statements
}
elseif ( condition )
{
block of statements
}
else
{
block of statements
}
The if statement consists of three sections:
if: This section is required. It tests a condition:
• If the condition is true: The block of statements is executed. After
the statements are executed, the script moves to the next instruction
following the conditional statement; if the conditional statement
contains any elseif or else sections, the script skips over
them.
• If the condition is not true: The block of statements is not executed.
The script skips to the next instruction, which can be an
elseif, an else, or the next instruction after the if conditional
statement.
elseif: This section is optional. You can use more than one elseif section
if you want. It also tests a condition:
• If the condition is true: The block of statements is executed.
After executing the block of statements, the script goes to the next
instruction following the conditional statement; if the if statement
141 Chapter 7: Controlling the Flow of the Script
contains any additional elseif sections or an else section, the
script skips over them.
• If the condition is not true: The block of statements is not executed.
The script skips to next instruction, which can be an elseif, an
else, or the next instruction after the if conditional statement.
else: This section is also optional. Only one else section is allowed.
This section does not test a condition, rather it executes the block of
statements. If the script has entered this section, it means that the if
section and all the elseif sections are not true.
Here’s an example. Pretend you’re a teacher. The following if statement,
when given a test score, sends your student a grade and a snappy little text
message. It uses all three sections of the if statement, as follows:
if ($score > 92 )
{
$grade = “A”;
$message = “Excellent!”;
}
elseif ($score <= 92 and $score > 83 )
{
$grade = “B”;
$message = “Good!”;
}
elseif ($score <= 83 and $score > 74 )
{
$grade = “C”;
$message = “Okay”;
}
elseif ($score <= 74 and $score > 62 )
{
$grade = “D”;
$message = “Uh oh!”;
}
else
{
$grade = “F”;
$message = “Doom is upon you!”;
}
echo $message.”\n”;
echo “Your grade is $grade\n”;
The if conditional statement proceeds as follows:
1. The value in $score is compared to 92.
If $score is greater than 92, $grade is set to A, $message is set to
Excellent!, and the script skips to the echo statement. If $score is 92
or less, $grade and $message are not set, and the script skips to the
elseif section.
142 Part III: Basic PHP Programming
2. The value in $score is compared to 92 and to 83.
If $score is 92 or less and greater than 83, $grade and $message are
set, and the script skips to the echo statement. If $score is 83 or less,
$grade and $message are not set, and the script skips to the second
elseif section.
3. The value in $score is compared to 83 and to 74.
If $score is 83 or less and greater than 74, $grade and $message are
set, and the script skips to the echo statement. If $score is 74 or less,
$grade and $message are not set, and the script skips to the next
elseif section.
4. The value in $score is compared to 74 and to 62.
If $score is 74 or less and greater than 62, $grade and $message are set,
and the script skips to the echo statement. If $score is 62 or less, $grade
and $message are not set, and the script skips to the else section.
5. $grade is set to F, and $message is set to Doom is upon you!.
The script continues to the echo statement.
When the block to be executed by any section of the if conditional statement
contains only one statement, the curly braces are not needed. For
example, say the preceding example had only one statement in the blocks,
as follows:
if ($grade > 92 )
{
$grade = “A”;
}
You could write it as follows:
if ($grade > 92 )
$grade = “A”;
This shortcut can save some typing, but when several if statements are
used, it can lead to confusion.
Negating if statements
You can write an if statement so that the statement block is executed when
the condition is false by putting an exclamation point (!) at the beginning of
the condition. For example, you can use the following if statement:
if (ereg(“^S[a-z]*”,$string))
{
$list[]=$string.”\n”;
}
143 Chapter 7: Controlling the Flow of the Script
This if statement creates an array of strings that begin with S. More specifically,
if $string matches a pattern that specifies one uppercase S at the
beginning, followed by a number of lowercase letters, the statement block is
executed. However, if you were to place an exclamation point at the beginning
of the condition, things would change considerably. For example, say
you use the following statements instead:
if (!egreg(“^S[a-z]*”,$string)
{
$list[]=$string.”\n”;
}
In this case, the array $list contains all the strings except those that begin
with S. In this case, because a ! appears at the beginning of the condition, the
condition is “$string does not match a pattern that begins with S.” So, when
$string does not begin with S, the condition is true.
Nesting if statements
You can have an if conditional statement inside another if conditional
statement. Putting one statement inside another is called nesting. For example,
suppose you need to contact all your customers who live in Idaho. You
plan to send e-mail to those who have e-mail addresses and send letters to
those who do not have e-mail addresses. You can identify the groups of customers
by using the following nested if statements:
if ( $custState == “ID” )
{
if ( $EmailAdd = “” )
{
$contactMethod = “letter”;
}
else
{
$contactMethod = “email”;
}
}
else
{
$contactMethod = “none needed”;
}
These statements first check to see if the customer lives in Idaho. If the customer
does live in Idaho, the script tests for an e-mail address. If the e-mail
address is blank, the contact method is set to letter. If the e-mail address
is not blank, the contact method is email. If the customer does not live in
Idaho, the else section sets the contact method to indicate that the customer
will not be contacted at all.
144 Part III: Basic PHP Programming
Using switch statements
For most situations, the if conditional statement works best. However,
sometimes you have a list of conditions and want to execute different statements
for each condition. For example, suppose your script computes sales
tax. How do you handle the different state sales tax rates? The switch statement
was designed for such situations.
The switch statement tests the value of one variable and executes the block
of statements for the matching value of the variable. The general format is as
follows:
switch ( $variablename )
{
case value :
block of statements;
break;
case value :
block of statements;
break;
…
default:
block of statements;
break;
}
The switch statement tests the value of $variablename. The script then
skips to the case section for that value and executes statements until it
reaches a break statement or the end of the switch statement. If there is no
case section for the value of $variablename, the script executes the default
section. You can use as many case sections as you need. The default section
is optional. If you use a default section, it’s customary to put the default section
at the end, but as far as PHP is concerned, it can go anywhere.
The following statements set the sales tax rate for different states:
switch ( $custState )
{
case “OR” :
$salestaxrate = 0;
break;
case “CA” :
$salestaxrate = 1.0;
break;
default:
$salestaxrate = .5;
break;
}
$salestax = $orderTotalCost * $salestaxrate;
In this case, the tax rate for Oregon is 0, the tax rate for California is 100 percent,
and the tax rate for all the other states is 50 percent. The switch statement
looks at the value of $custState and skips to the section that matches
the value. For example, if $custState is TX, the script executes the default
section and sets $salestaxrate to .5. After the switch statement, the
script computes $salestax at .5 times the cost of the order.
The break statements are essential in the case section. If a case section
does not include a break statement, the script does not stop executing at
the end of the case section. The script continues executing statements past
the end of the case section, on to the next case section, and continues until
it reaches a break statement or the end of the switch statement. This is a
problem for every case section except the last one because it will execute
sections following the appropriate section.
The last case section in a switch statement doesn’t actually require a break
statement. You can leave it out. However, it’s a good idea to include it for clarity
and consistency.
Repeating Actions by Using Loops
Loops are used frequently in scripts to set up a block of statements that
repeat. The loop can repeat a specified number of times. For example, a loop
that echoes all the state capitals needs to repeat 50 times. Or the loop can
repeat until a certain condition is met. For example, a loop that echoes the
names of all the files in a directory needs to repeat until it runs out of files,
regardless of how many files there are. Here are three types of loops:
A for loop: Sets up a counter; repeats a block of statements until the
counter reaches a specified number
A while loop: Sets up a condition; checks the condition, and if it’s true,
repeats a block of statements until the condition becomes false
A do..while loop: Sets up a condition; executes a block of statements;
checks the condition; if the condition is true, repeats the block of statements
until the condition becomes false
I describe each of these loops in detail in the following few sections.
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146 Part III: Basic PHP Programming
Using for loops
The most basic for loops are based on a counter. You set the beginning value
for the counter, set the ending value, and set how the counter is incremented
each time the statement block is executed. The general format is as follows:
for (startingvalue;endingcondition;increment)
{
block of statements;
}
Within the for statement, you need to fill in the following values:
startingvalue: The startingvalue is a statement that sets up a variable
to be your counter and sets it to your starting value. For example,
the statement $i=1; sets $i as the counter variable and sets it equal to 1.
Frequently, the counter variable is started at 0 or 1. The starting value can
be a number, a combination of numbers (like 2 + 2), or a variable.
endingcondition: The endingcondition is a statement that sets your
ending value. As long as this statement is true, the block of statements
keeps repeating. When this statement is not true, the loop ends. For
example, the statement $i<10; sets the ending value for the loop to 10.
When $i is equal to 10, the statement is no longer true (because $i is no
longer less than 10), and the loop stops repeating. The statement can
include variables, such as $i<$size;.
increment: A statement that increments your counter. For example, the
statement $i++; adds 1 to your counter at the end of each block of statements.
You can use other increment statements, such as $i=+1; or $i—;.
A basic for loop sets up a variable, like $i, that is used as a counter. This
variable has a value that changes during each loop. The variable $i can be
used in the block of statements that is repeating. For example, the following
simple loop displays Hello World! three times:
for ($i=1;$i<=3;$i++)
{
echo “$i. Hello World!<br>”;
}
The statements in the block do not need to be indented. PHP doesn’t care
whether they’re indented. However, indenting the blocks makes it much
easier for you to understand the script.
The following is the output from these statements:
1. Hello World!
2. Hello World!
3. Hello World!
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Nesting for loops
You can nest for loops inside of for loops. Suppose you want to print out
the times tables from 1 to 9. You can use the following statements:
for($i=1;$i<=9;$i++)
{
echo “\nMultiply by $i \n”;
for($j=1;$j<=9;$j++)
{
$result = $i * $j;
echo “$i x $j = $result\n”;
}
}
The output is as follows:
Multiply by 1
1 x 1 = 1
1 x 2 = 2
…
1 x 8 = 8
1 x 9 = 9
Multiply by 2
2 x 1 = 2
2 x 2 = 4
…
2 x 8 = 16
2 x 9 = 18
Multiply by 3
3 x 1 = 3
and so on.
Designing advanced for loops
The structure of a for loop is quite flexible and allows you to build loops for
almost any purpose. A for loop has this general format:
for (beginning statements; conditional statements; ending
statements)
{
block of statements;
}
The statements within a for loop have the following roles:
The beginning statements execute once at the start of the loop. They
can be statements that set any needed starting values or other statements
that you want to execute before your loop starts running.
148 Part III: Basic PHP Programming
The conditional statements are tested for each iteration of your loop.
The ending statements execute once at the end of the loop. They can be
statements that increment your values or any other statements that you
want to execute at the end of your loop.
Each statement section is separated by a semicolon (;). Each section can contain
as many statements as needed, separated by commas. Any section can
be empty.
The following loop has statements in all three sections:
$t = 0;
for ($i=0,$j=1;$t<=4;$i++,$j++)
{
$t = $i + $j;
echo “$t<br>”;
}
The two statements in the first section are the beginning statements; the conditional
statement in the second section is the conditional statements; and
the two statements in the third section are the ending statements.
The output of these statements is as follows:
135
The loop is executed in the following order:
1. The beginning section containing two statements is executed.
$i is set to 0, and $j is set to 1.
2. The conditional section containing one statement is evaluated.
Is $t less than or equal to 4? Yes, so the statement is true. The loop continues
to execute.
3. The statements in the statement block are executed.
$t becomes equal to $i plus $j, which is 0 + 1, which equals 1. Then $t
is echoed to give the output 1.
4. The ending section containing two statements ($i++ and $j++) is
executed.
Both $i and $j are incremented by one, so $i now equals 1, and $j now
equals 2.
5. The conditional section is evaluated.
Is $t less than or equal to 4? Because $t is equal to 1 at this point, the
statement is true. The loop continues to execute.
149 Chapter 7: Controlling the Flow of the Script
6. The statements in the statement block are executed.
$t becomes equal to $i plus $j, which is 1 + 2, which equals 3. Then $t
is echoed to give the output 3.
7. The ending section containing two statements ($i++ and $j++) is
executed.
Both $i and $j are incremented by one, so $i now equals 2, and $j now
equals 3.
8. The conditional section is evaluated.
Is $t less than or equal to 4? Because $t now equals 3, the statement is
true. The loop continues to execute.
9. The statements in the statement block are executed.
$t becomes equal to $i plus $j, which is 2 + 3, which equals 5. Then $t
is echoed to give the output 5.
10. The ending section containing two statements ($i++ and $j++) is
executed.
Both $i and $j are incremented by 1, so $i now equals 2, and $j now
equals 3.
11. The conditional section is evaluated.
Is $t less than or equal to 4? Because $t now equals 5, the statement is
not true. The loop does not continue to execute. The loop ends, and the
script continues to the next statement after the end of the loop.
Using while loops
A while loop continues repeating as long as certain conditions are true. The
loop works as follows:
1. You set up a condition.
2. The condition is tested at the top of each loop.
3. If the condition is true, the loop repeats. If the condition is not true, the
loop stops.
The following is the general format of a while loop:
while ( condition )
{
block of statements
}
150 Part III: Basic PHP Programming
The following statements set up a while loop that looks through an array for
an apple:
$fruit = array ( “orange”, “apple”, “grape” );
$testvar = “no”;
$k = 0;
while ( $testvar != “yes” )
{
if ($fruit[$k] == “apple” )
{
$testvar = “yes”;
echo “apple\n”;
}
else
{
echo “$fruit[$k] is not an apple\n”;
}
$k++;
}
These statements generate the following output:
orange is not an apple
apple
The script executes the statements as follows:
1. The variables are set before starting the loop.
$fruit is an array with three values, $testvar is a test variable set to
“no”, and $k is a counter variable set to 0.
2. The loop starts by testing whether $testvar != “yes” is true.
Because $testvar was set to “no”, the statement is true, so the loop
continues.
3. The condition in the if statement is tested.
Is $fruit[$k] == “apple” true? At this point, $k is 0, so the script
checks $fruit[0]. Because $fruit[0] is “orange”, the statement is
not true. The statements in the if block are not executed, so the script
skips to the else statement.
4. The statement in the else block is executed.
The else block outputs the line “orange is not an apple”. This is
the first line of the output.
5. $k is incremented by one.
Now $k becomes equal to 1.
151 Chapter 7: Controlling the Flow of the Script
6. The bottom of the loop is reached.
Flow returns to the top of the loop.
7. The condition $testvar != “yes” is tested again.
Is $testvar != “yes” true? Because $testvar has not been changed
and is still set to “no”, it is true, so the loop continues.
8. The condition in the if statement is tested again.
Is $fruit[$k] == “apple” true? At this point, $k is 1, so the script
checks $fruit[1]. Because $fruit[1] is “apple”, the statement is
true. So the loop enters the if block.
9. The statements in the if block are executed.
These statements set $testvar to “yes” and output “apple”. This is
the second line of the output.
10. $k is incremented again.
Now $k equals 2.
11. The bottom of the loop is reached again.
Once again, the flow returns to the top of the loop.
12. The condition $testvar != “yes” is tested one last time.
Is $testvar != “yes” true? Because $testvar has been changed and
is now set to “yes”, it is not true. The loop stops.
It’s possible to write a while loop that is infinite — that is, a loop that loops
forever. You can easily, without intending to, write a loop in which the condition
is always true. If the condition never becomes false, the loop never ends.
For a discussion of infinite loops, see the section “Avoiding infinite loops,”
later in this chapter.
Using do..while loops
A do..while loop is very similar to a while loop. Like a while loop, a
do..while loop continues repeating as long as certain conditions are true.
Unlike while loops, however, those conditions are tested at the bottom of
each loop. If the condition is true, the loop repeats. When the condition is
not true, the loop stops.
The general format for a do..while loop is as follows:
do
{
block of statements
} while ( condition );
152 Part III: Basic PHP Programming
The following statements set up a loop that looks for an apple. This script
does the same thing as the script in the preceding section that uses a while
loop:
$fruit = array ( “orange”, “apple”, “grape” );
$testvar = “no”;
$k = 0;
do
{
if ($fruit[$k] == “apple” )
{
$testvar = “yes”;
echo “apple\n”;
}
else
{
echo “$fruit[$k] is not an apple\n”;
}
$k++;
} while ( $testvar != “yes” );
The output of these statements in a browser is as follows:
orange is not an apple
apple
This is the same output shown for the while loop example. The difference
between a while loop and a do..while loop is where the condition is checked.
In a while loop, the condition is checked at the top of the loop. Therefore, the
loop will never execute if the condition is never true. In the do..while loop,
the condition is checked at the bottom of the loop. Therefore, the loop always
executes at least once, even if the condition is never true.
For example, in the preceding loop that checks for an apple, suppose the
original condition is set to yes, instead of no, by using this statement:
$testvar = “yes”;
The condition tests false from the beginning. It is never true. In a while loop,
there is no output. The statement block never runs. However, in a do..while
loop, the statement block runs once before the condition is tested. Thus, the
while loop produces no output, but the do..while loop produces the following
output:
orange is not an apple
The do..while loop produces one line of output before the condition is
tested. It does not produce the second line of output because the condition
tests false.
153 Chapter 7: Controlling the Flow of the Script
Avoiding infinite loops
You can easily set up loops so that they never stop. These are called infinite
loops. They repeat forever. However, seldom does anyone create an infinite
loop intentionally. It is usually a mistake in the programming. For example,
a slight change to the script that sets up a while loop can make it into an
infinite loop.
Here is the script shown in the section, “Using while loops,” earlier in this
chapter, with a slight change:
$fruit = array ( “orange”, “apple”, “grape” );
$testvar = “no”;
while ( $testvar != “yes” )
{
$k = 0;
if ($fruit[$k] == “apple” )
{
$testvar = “yes”;
echo “apple\n”;
}
else
{
echo “$fruit[$k] is not an apple\n”;
}
$k++;
}
The small change is moving the statement $k = 0; from outside the loop to
inside the loop. This small change makes it into an endless loop. This changed
script has the following output:
orange is not an apple
orange is not an apple
orange is not an apple
orange is not an apple
…
This will repeat forever. Every time the loop runs, it resets $k to 0. Then it
gets $fruit[0] and echoes it. At the end of the loop, $k is incremented to 1.
However, when the loop starts again, $k is set back to 0. Consequently, only
the first value in the array, orange, is ever read. The loop never gets to the
apple, and $testvar is never set to “yes”. The loop is endless.
Don’t be embarrassed if you write an infinite loop. I guarantee that the best
programming guru in the world has written many infinite loops. It’s not a big
deal. If you are testing a script and get output repeating endlessly, there’s no
need to panic. Do one of the following:
154 Part III: Basic PHP Programming
If you’re using PHP on a Web page: Wait. It will stop by itself in a short
time. The default time is 30 seconds, but the timeout period may have
been changed by the PHP administrator. You can also click the Stop
button on your browser to stop the display in your browser.
If you’re using PHP CLI: Press Ctrl + C. This stops the script from running.
Sometimes the output will continue to display a little longer, but it
will stop very shortly.
Then figure out why the loop is repeating endlessly and fix it.
A common mistake that can result in an infinite loop is using a single equal
sign (=) when you mean to use double equal signs (==). The single equal sign
stores a value in a variable; the double equal signs test whether two values
are equal. The following condition using a single equal sign is always true:
while ($testvar = “yes”)
The condition simply sets $testvar equal to “yes”. This is not a question
that can be false. What you probably meant to write is this:
while ($testvar == “yes”)
This is a question asking whether $testvar is equal to “yes”, which can be
answered either true or false.
Another common mistake is to leave out the statement that increments the
counter. For example, in the script earlier in this section, if you leave out the
statement $k++;, $k is always 0, and the result is an infinite loop.
Breaking out of a loop
Sometimes you want your script to break out of a loop. PHP provides two
statements for this purpose:
break: Breaks completely out of a loop and continues with the script
statements after the loop.
continue: Skips to the end of the loop where the condition is tested.
If the condition tests positive, the script continues from the top of the
loop.
The break and continue statements are usually used in conditional statements.
In particular, break is used most often in switch statements, discussed
earlier in this chapter.
155 Chapter 7: Controlling the Flow of the Script
The following statements show the difference between continue and break.
This first section is an example of the break statement:
$counter = 0;
while ( $counter < 5 )
{
$counter++;
If ( $counter == 3 )
{
echo “break\n”;
break;
}
echo “Last line in loop: counter=$counter\n”;
}
echo “First line after loop\n\n”;
The output of this statement is the following:
Last line in loop: counter=1
Last line in loop: counter=2
break
First line after loop
Notice that the first loop ends at the break statement. It stops looping and
jumps immediately to the statement after the loop. That’s not true of the
continue statement.
The following section is an example of the continue statement:
$counter = 0;
while ( $counter < 5 )
{
$counter++;
If ( $counter == 3 )
{
echo “continue\n”;
continue;
}
echo “Last line in loop: counter=$counter\n”;
}
echo “First line after loop\n”;
The output of this statement is the following:
Last line in loop: counter=1
Last line in loop: counter=2
continue
Last line in loop: counter=4
Last line in loop: counter=5
First line after loop
156 Part III: Basic PHP Programming
Unlike the break statement loop, this loop does not end at the continue
statement. It just stops the third repeat of the loop and jumps back up to the
top of the loop. It then finishes the loop, with the fourth and fifth repeats,
before it goes to the statement after the loop.
One use for break statements is insurance against infinite loops. The following
statements inside a loop can stop it at a reasonable point:
$test4infinity++;
if ($test4infinity > 100 )
{
break;
}
If you’re sure that your loop should never repeat more than 100 times, these
statements will stop the loop if it becomes endless. Use whatever number
seems reasonable for the loop you’re building.
Chapter 8
Reusing PHP Code
In This Chapter
Including files in scripts
Understanding security for included files
Writing functions
Using functions
Often scripts need to perform the same actions in several different locations
in the script. For example, a script may need to get data from a
database several different times. It may even be the case that you use the
same code in different scripts. If you find yourself typing the same ten lines of
code over and over (or cutting and pasting it repeatedly), you can move that
code into a separate file and get it from that file whenever you need it. Here
are several reasons to reuse code:
Less typing: Less work is always a good reason for anything.
Debug once: You can write the code once, debug it so you know it works,
and then use it whenever you need it. It’s rare to write code that doesn’t
have a typo or two in it, let alone occasional peculiar logic, so code always
has to be debugged. It saves time to use proven code when possible,
instead of writing new code that will have to be debugged.
Easier to understand: A shorter script that is less cluttered with code is
easier for people to read and understand. For example, one line in your
script that says getData() is easier to understand than the ten lines
that actually get the data.
Easier to maintain: If you reuse code and you need to change something
in the code, you only need to change it in one external file, instead of
having to find and change it in a dozen places in your script. For example,
if you change the name of your database, you can change the name
in one file, rather than having to change it repeatedly in many scripts.
You can reuse code two ways: by inserting a file containing code into a script
or by writing and calling a function. In this chapter, you find out how to use
both methods.
Inserting Code in Your Script
You can put as many lines of code as you need into a file, separate from your
script, and include that file in the script wherever you need it. PHP provides
the include statement to insert code where it’s needed.
Including files
Suppose you’re writing an online product catalog and your application contains
many pages that display pictures of your products. You can define the
height and width for the pictures in constants and use the constants in your
HTML image tags, thereby displaying all your pictures consistently. By using
constants, you can change the size of the graphics simply by changing the
constant definition; you don’t have to change every image tag in your script.
You can define these constants by using the following statements in the top
of your script:
define(“HEIGHT”,60);
define(“WIDTH”,60);
You can then use the constants in your HTML image tags as follows:
<img src=”mypic.jpg” height=”<?php echo HEIGHT?>”
width=”<?php echo WIDTH?>” />;
If you display the product pictures in many different scripts, you don’t have to
add the define statements in the top of every script. Instead, you can put the
statements into a separate file and include the file in the top of the scripts.
You can create a file called size.inc (you can use any extension for include
files, but .inc is often used by convention) that contains the following:
<?php
define(“HEIGHT”,60);
define(“WIDTH”,60);
?>
You can then include the file at the top of each script with the following
statement:
include(“size.inc”);
When PHP sees the include statement, it reads the code from the file so the
code is inserted at the location where the include statement is used. That
means that the constants are defined when size.inc is included, and the
image tags in your file will be output as follows:
<img src=”mypic.jpg” height=”60” width=”60” />
158 Part III: Basic PHP Programming
This HTML code displays the image on your Web page. If you want to change
the height or width at any time, just change the definitions of HEIGHT and
WIDTH in size.inc, and all the images will automatically change size. Actually,
because the image tag that displays the picture is rather complex, you could
put the image statement into a file called displayPix.inc and include the file
whenever you want to display an image. You could have the image tag alone
in displayPix.inc and include both size.inc and displayPix.inc at the
beginning of each script, or you could include size.inc in displayPix.inc
and only include displayPix.inc in your script.
Forgetting the PHP tags in the include file is a common mistake. It’s also a
security problem because without the PHP tags, the code in the file is displayed
to the user as HTML. If the user sees the size of the graphic files, it’s
not much of a problem. However, suppose you had the password for your
database in the include file — that would be a problem.
Instead of the standard include statement, you can use the following similar
statement:
include_once(“filename”);
This statement prevents included files with similar variables from overwriting
each other. For example, you can use include_once to include your function
definitions (which are discussed later in this chapter) to be sure that
they are only defined once.
PHP also provides the require and require_once statements that work just
like include statements, differing only in the way errors are handled. This difference
arises when you use an include or a require statement that calls a
file that doesn’t exist. If you require a file that doesn’t exist, it is a fatal error,
and your script stops running. If you include a file that doesn’t exist, you only
receive a warning, and the script continues to run.
You can use a variable name for the filename as follows:
include (“$filename”);
For example, you might want to display different messages on different days:
You might store these messages in files that are named for the day on which
the message should display. For example, you could have a file named
Sun.inc with the following contents:
echo “Go ahead. Sleep in. No work today.”;
And similar files for all days of the week. The following statements can be
used to display the correct message for the current day:
$today = date(“D”);
include(“$today”.”inc”);
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After the first statement, $today contains the day of the week in abbreviation
form. The date statement is discussed in Chapter 5. The second statement
includes the correct file, using the day stored in $today. If $today contains
Sun, the statement includes a file called Sun.inc.
Storing include files
Where you store include files can be a security issue, especially for Web sites.
Files stored on Web sites can be downloaded by any user, unless the files are
protected. Theoretically, a user could connect to your Web site by using the
following type of URL:
http://yourdomain.com/secretpasswords.inc
Suppose you happen to have a file in your Web space named
secretpasswords.inc that contains the following statements:
<?php
$mysecretaccount=”account48756”;
$mypassword=”secret”;
?>
In most cases, the Web server is not configured to process PHP sections in
files with any extensions other than PHP. Therefore, the Web server would
not process these statements. Instead, it would obligingly display the contents
of secretpasswords.inc to the user, as if the lines were HTML code.
You can protect against this in one of the following ways:
Name include files with .php extensions. The Web server will then
process the PHP sections, rather than treat them the same as the HTML
sections. However, you need to think carefully about the contents of the
include files if you name them with a .php extension. In some cases, running
the PHP sections in an include file independently, without the context
provided when they are run by including them in a script, can be a
problem. For example, suppose you had code in your include file that
deleted a record in the database (highly unlikely). Running the code outside
of a script might have negative consequences. Another drawback is
that it can be convenient to name files with an .inc extension so you
can see at a glance that the file is a fragment, not a script intended to
run by itself.
Configure the Web server to scan for PHP sections in files with the
.inc extension, as well as the .php extension. This allows you to recognize
include files by their name. However, you still have the problem
of possible unintended consequences of running the file independently,
as discussed in the preceding bullet.
160 Part III: Basic PHP Programming
Store the file in a location that is not accessible to outside users. This
is the preferred solution, but it may not be possible in some environments,
such as when you’re using a Web hosting company.
The best place to store include files is in a directory that outside users can’t
access. For example, for your Web site, you can set up an include directory
that is outside your Web space. That is, you can create a directory in a location
that outside users can’t access with their browsers. For example, the default
Web space for Apache — unless it has been changed in the configuration file
(usually called httpd.conf) — is apache/htdocs. If you store your include
files in a directory that is not in your Web space, such as d:\include, you can
protect the files from outside users.
Setting up include directories
You can set up an include directory where PHP looks for any files specified
in an include statement. If you are the PHP administrator, you can set up an
include directory in the php.ini file (the PHP configuration file in your system
directory, as described in Appendix A). Find the setting for include_path and
change it to the path to your preferred directory. If there is a semicolon at the
beginning of the line, before include_path, remove it. The following are examples
of include_path settings in the php.ini file:
include_path=”.;d:\include”; # for Windows
include_path=”.:/user/local/include”; # for Unix/Linux/Mac
Both of these statements specify two directories where PHP looks for include
files. The first directory is dot (meaning the current directory), followed by
the second directory path. You can specify as many include directories as you
want, and PHP will search them for the include file in the order in which they
are listed. The directory paths are separated by a semicolon for Windows and
a colon for Unix/Linux.
If you don’t have access to php.ini, you can set the path in each individual
script by using the following statement:
ini_set(“include_path”,”d:\hidden”);
This statement sets the include_path to the specified directory only while
the script is running. It doesn’t set the directory for your entire Web site.
To access a file from an include directory, just use the file name, as follows.
You don’t need to use the full path name.
include(“secretpasswords.inc”);
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If your include file is not in an include directory, you may need to use the
entire path name in the include statement. If the file is in the same directory
as the script, the file name alone is sufficient. However, if the file is located in
another directory, such as a subdirectory of the directory the script is in or a
hidden directory outside the Web space, you need to use the full path name
to the file, as follows:
include(“d:/hidden/secretpasswords.inc”);
Creating Reusable Code (Functions)
Applications often perform the same task at different points in the script or in
different scripts. This is when functions come in handy. A function is a group
of PHP statements that perform a specific task. You can use the function
wherever you need to perform the task.
For example, suppose you add a footer to the bottom of every Web page by
using the following statements:
.
echo ‘<img src=”greenrule.jpg” width=”100%” height=”7” />
<address>My Great Company
<br />1234 Wonderful Rd.
<br />San Diego, CA 92126
</address></font>
<p>or send questions to
<a href=”mailto:sales@company.com”>sales </a>
<img src=”greenrule.jpg” width=”100%” height=”7” />’;
It’s not uncommon for Web pages to have headers or footers much longer
than this. So, rather than type this code into the bottom of every Web page,
probably incurring at least a couple of typos in the process, you can create a
function that contains the preceding statements and name it add_footer.
Then at the end of every page, you can just use the function (a process
referred to as calling the function) that contains the footer statements. The
code for this simple function call is as follows:
add_footer();
Notice the parentheses after the function name. These are required in a function
call because they tell PHP that this is a function.
162 Part III: Basic PHP Programming
Defining functions
You can create a function by putting the code into a function block. The general
format is as follows:
function functionname()
{
block of statements;
return;
}
For example, you create the function add_footer() that I discuss in the preceding
section with the following statements:
function add_footer()
{
echo ‘<img src=”greenrule.jpg” width=”100%” height=”7” />
<address>My Great Company
<br />1234 Wonderful Rd.
<br />San Diego, CA 92126
</address></font>
<p>or send questions to
<a href=”mailto:sales@company.com”>sales </a>
<img src=”greenrule.jpg” width=”100%” height=”7” />’;
return;
}
The return statement stops the function and returns to the main script. (The
return statement at the end of the function is not required, but it makes the
function easier to understand. The return statement is discussed in more
detail in the section “Returning a value from a function,” later in this chapter.)
You can write a function anywhere in the script, but the usual practice is to
put all the functions together at the beginning or the end of the script file.
Functions that you plan to use in more than one script can be in a separate
file, and you can include the file in any scripts that need to use the functions.
At this point, you’re probably wondering, “Why can’t I just put the footer statements
into a separate file called footer.inc and include footer.inc at the
end of each Web page?” Good question! Actually, you can. In fact, you should.
In this case, the instructions for creating the footer consist of a simple block
of statements that echo static HTML code. You could just put the HTML in the
include file and include it at the end of the page. You wouldn’t even need to use
PHP tags in the include file.
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However, suppose the company has three divisions and you want to include
the division name in the footer and have the e-mail address send the e-mail
to the appropriate division. You could write three different include files and
include the correct one. However, a function works better in this situation
because functions are more flexible and faster. You can send information to
the function (called passing values), telling it which division to use in the
output. The function looks like this:
function add_footer($division)
{
echo ‘<img src=”greenrule.jpg” width=”100%” height=”7” />
<p>’.$division.’ Division</p>
<address>My Great Company
<br />1234 Wonderful Rd.
<br />San Diego, CA 92126
</address></font>
<p>or send questions to
<a href=”mailto:’.$division.’@company.com”>’
.$division.’</a>
<img src=”greenrule.jpg” width=”100%” height=”7” />’;
return;
}
In this version, the function is expecting a value to be passed to it. It stores
the passed value in a variable called $division and uses the variable for the
text that needs to change. When you use this function, you must pass it a
value, as follows:
add_footer(“Sales”);
You can change the division by calling the function with a different value:
add_footer(“Accounting”);
Notice the format of the echo statement. The string is enclosed in single
quotes. In the previous function, without variables, the format was simple —
just a single quote at the beginning and another single quote at the end. In
this function example, using a variable, the quoted string is ended when
$division is used and reopened after the variable. Remember, variables are
not evaluated inside single quotes. If $division were used inside single
quotes, the output would show $division Division, instead of Sales
Division.
You can pass a value back from a function, called returning a value. Values are
returned by using the return statement. For example, suppose you want the
function to put the footer into a variable rather than echo the footer. In that
case, the function looks like this:
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function add_footer($division)
{
$str=’<img src=”greenrule.jpg” width=”100%” height=”7” />
<p>’.$division.’ Division</p>
<address>My Great Company
<br />1234 Wonderful Rd.
<br />San Diego, CA 92126
</address></font>
<p>or send questions to
<a href=”mailto:’.$division.’@company.com”>’
.$division.’</a>
<img src=”greenrule.jpg” width=”100%” height=”7” />’;
return $str;
}
In this case, you could use these statements:
$footer = add_footer(“Sales”);
echo $footer;
When you echo $footer, you output the entire footer string that was created
in the function.
The rest of this chapter describes in detail how to create and use functions.
A good programmer looks for opportunities to put script code into functions,
which improves readability and maintainability, as well as makes the script
run faster.
Using variables in functions
You can create and use a variable inside your function. Such a variable is
called local to the function A local variable is not available outside of the
function, so it’s not available to the main script. (If you want to use the variable
outside the function, you have to make the variable global, rather than
local, by using a global statement.) For example, the variable $name is created
in the following function:
function format_name($first_name,$last_name)
{
$name = $last_name.”, “.$first_name;
}
You can then call the function, passing it values, and attempt to echo the
value of the variable $name:
format_name(“Jess”,”Jones”);
echo “$name”;
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However, these statements do not produce any output. In the echo statement,
$name doesn’t contain any value. The variable $name was created
inside the function, so it doesn’t exist outside the function.
You can create a variable inside a function that does exist outside the function
by using the global statement. The following statements contain the
same function with a global statement added:
function format_name($first_name,$last_name)
{
global $name;
$name = $last_name.”, “.$first_name;
}
You can now call the function, passing it the same values, and echo the value
of the variable $name:
format_name(“Jess”,”Jones”);
echo “$name”;
The script now echoes the value of the variable $name:
Jones, Jess
You must make the variable global before you can use it. If the global statement
follows the $name assignment statement, the script does not produce
any output. That is, in the preceding function, if the global statement followed
the $name = statement, the function wouldn’t work correctly.
Similarly, if a variable is created outside the function, you can’t use it inside
the function unless it is global. You can make the variable global as shown in
the following statements:
$first_name = “Jess”;
$last_name = “Jones”;
function format_name()
{
global $first_name, $last_name;
$name = $last_name.”, “.$first_name;
echo “$name”;
}
format_name();
If you don’t use the global statement, $last_name and $first_name inside
the function are different variables than $last_name and $first_name created
outside the script. The local variables $last_name and $first_name
inside the function are created when you name them and have no values.
Therefore, $name would echo only a comma.
You need the global statement for the function to work correctly.
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Passing values to a function
You pass values to a function by putting the values between the parentheses
when you call the function, as follows:
functionname(value1,value2,…);
Of course, the variables can’t just show up. The function must be expecting
them. The function statement includes variable names for the values it’s
expecting, as follows:
function functionname($varname1,$varname2,…)
{
statements
return;
}
Passing the right type of values
Values can be variables or values, including values that are computed. The
values passed can be any type of data, including arrays or objects (objects
are discussed in Chapter 9).
The following statements call a function that computes the sales tax. A
salestax function needs to know the amount of the purchase, so it can
compute the amount of tax. It also needs to know the state, so it can use the
correct tax rate to compute the sales tax. The values you need to pass are a
number (the purchase amount) and a string (the state’s name). The following
calls are valid:
compute_salestax(2000,”CA”); This function is being passed two
values, 2000 and CA, CA.
compute_salestax(2*1000,””); This function is being passed two
values, 2000 and ???, an empty value. The function must include code
that handles the empty variable.
compute_salestax(2000,”C”.”A”); This function is being passed two
values, 2000 and ???, CA.
You can pass arrays to functions. (Arrays are discussed in Chapter 6.) For
example, the following function uses an array that is passed to it:
function add_numbers($numbers)
{
for($i=0;$i <sizeof($numbers);$i++)
{
@$sum = $sum + $numbers[$i];
}
return $sum;
}
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This function adds all the numbers passed to it in an array of numbers. If the
value passed to it is not an array, PHP stores the value in $numbers as its correct
data type — an integer or a string. When the function gets to the statement
sizeof($numbers), it fails because $numbers is not an array and sizeof
requires an array. A well-written function checks the values that are passed to
it make sure they are the type of value needed before executing the statements
in the function. For example, the following statement can be added to the function
block, immediately before the for statement:
If(!is_array($numbers)
{
echo “The value passed is not an array”;
exit();
}
Similarly, this function should check whether the elements of the array are
numbers, using some of the functions described in Chapter 5.
You can use the following statements to define an array that is then passed to
the add_numbers function:
$arrayofnumbers = array(100,200);
$total = add_numbers($arrayofnumbers);
After these statements, $total equals 300.
Passing values in the correct order
The function receives the values in the order they are passed. That is, suppose
you have the following function:
function functionx($x,$y,$z)
{
do stuff
}
You call the function as follows:
functionx($var1,$var2,$var3);
The function sets $x=$var1, $y=$var2, and $z=$var3.
If the values you pass aren’t in the expected order, the function uses the wrong
value when performing the task. For example, suppose that your definition for
a function to compute sales tax looks like the following:
function compute_salestax($orderCost,$custState)
{
compute tax
}
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But suppose you call it by using the following call:
compute_salestax($custState,$orderCost);
The function uses the state as the cost of the order, which it sets to 0 because
it is a string. It sets the state to the number in $orderCost, which would not
match any of its categories. The output would be 0.
Passing the right number of values
A function is designed to expect a certain number of values to be passed to
it. If you don’t send enough values, the function sets the missing one(s) to
NULL. If you have your warning message level turned on, a warning message
is displayed. (See Chapter 4 for a description of error levels.) For example,
you might see a message similar to the following:
Warning: Missing argument 2 for format_name() in testing.php
on line 9
Remember, warnings don’t stop the script; it continues to run. Suppose that
you call the format_name function described in the section “Using variables
in functions,” earlier in this chapter, by using the following statement:
format_name(“Jess”);
The output is as follows:
Jess,
If you send too many values, the function ignores the extra values. In most
cases, you do not want to pass the wrong number of values.
You can set default values to be used when a value isn’t passed. The defaults
are set when you write the function, be assigning a default value for the value(s)
it is expecting, as follows:
function add_2_numbers($num1=1,$num2=1)
{
$total = $num1 + $num2;
return $total;
}
If one or both values are not passed, the function uses the assigned defaults.
But if a value is passed, it is used instead of the default. For example, you
could use one of the following calls:
add_2_numbers(2,2);
add_2_numbers(2);
add_2_numbers();
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The result are, in consecutive order:
$total = 4
$total = 3
$total = 2
The first $total is 4, because 2 and 2 are passed. The second $total is
three because 2 is passed and the default 1 is used for $num2. The third
$total is 2 because neither value is passed and, therefore, the defaults of 1
are used for both $num1 and $num2.
Passing values by reference
When you pass values into variables in the function definition, you are passing
by value. Passing by value is the most common way to pass values to a
function, as in the following example:
function add_1($num1)
{
$num1 = $num1 + 1;
}
When passing by value, a copy is made of a value and the copy is passed
to the function. The value passed into the function is stored in the variable
$num1, and 1 is added to it in the function. However, the value of the variable
outside the function is not changed. Suppose that you call the function with
the following statements:
$orig_num = 3;
add_1($orig_num);
echo $orig_num;
The output from the echo statement is 3. A copy of the value stored in
$orig_num was passed to add_1, but nothing in the function affected
$orig_num. It is unchanged. You can change $orig_num by adding a return
statement to the function, as follows:
return $num1;
You then store the returned value in $orig_num as follows:
$orig_num = 3;
$orig_num = add_1($orig_num);
echo $orig_num;
Now, the echo statement outputs 4.
In some cases, you may want to change the values of variables directly, changing
their values outside the function. That is, in the first example above, you
may want $orig_value changed from inside the function, without having to
170 Part III: Basic PHP Programming
pass it back. In this simple case, you could make the variable global, but you
can also do it using a technique called passing by reference. To pass a variable
by reference, add & before the variable name, as follows:
function add_1(&$num1)
{
$num1 = $num1 + 1;
}
When you call this function, a value is passed that tells PHP where the variable
is stored, (that is, a pointer to the container called $orig_num where the
value 3 is stored) rather than a copy of the value. The variable $num1 then
becomes another name for $orig_num, rather than a different variable that
contains 3. When you assign something to $num1, it is stored in $orig_num.
$num1 and $orig_num are two names for the same storage location. When
you change the variable by using statements inside the function, the value at
the original location is changed as well. For example, suppose you call the
function by using the following statements:
$orig_num = 3;
add_1($orig_num);
echo $orig_num;
The output of the echo statement is 4.
Because you’re passing a pointer to a variable, the following doesn’t make
sense:
add_1(&7);
Passing by reference is used mainly when passing really large values, such as
an object or a large array. It’s more efficient to pass a pointer than to pass a
copy of really large values.
Returning a value from a function
If you want a function to send a value back to the main script, you use the
return statement. The main script can put the returned value in a variable
or use it in any manner it would use any value.
A return statement returns any values specified and ends the function,
returning to the main script. The general format is as follows:
return value;
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For example, the add2numbers function looks like this:
function add_2_numbers($num1,$num2)
{
$total = $num1 + $num2;
return $total;
}
The total of the two numbers is returned and the function ends. You call the
function as follows:
$sum = add_2_numbers(5,6);
$sum then equals the value in $total that was returned from the function,
which is 11 in this case. In fact, you could use a shortcut when defining the
function and send the total back to the main script with one statement:
return $num1 + $num2;
The main script can use the value in any of the usual ways. The following
statements use the function call in valid ways:
$total_height = add_2_numbers($height1,$height2);
$totalSize = $current_size + add_2_numbers($size1,$size2);
if (add_2_numbers($costSocks,$costShoes) > 200.00 )
$echo “No sale”;
A return statement can return only one value. However, the value returned
can be an array, so you can actually return many values from a function.
You can use a return statement in a conditional statement to end a function,
as follows:
function find_value($array,$value)
{
for($i=1;$i<sizeof($array);$i++)
{
if($array[$i] = $value)
{
echo “$i. $array[$i]<br>”;
return;
}
}
}
172 Part III: Basic PHP Programming
The function checks an array to see if it contains a particular value. For example,
you can call the function with the following statements:
$names = array(“Joe”,”Sam”,”Juan”);
find_value($names,”Sam”);
The function searches through the values in the array looking for Sam. If it
finds Sam, it stops searching. The output shows the array item where Sam
is found, as follows:
1. Sam
Often functions are designed to return Boolean values, as in the following
function:
function is_over_100($number)
{
if($number > 100)
{
return TRUE;
}
else {
return FALSE;
}
}
Numbers 100 or less return FALSE; numbers over 100 return TRUE.
Another common function design returns a value if the function succeeds,
but returns FALSE if the function does not succeed. For example, you could
design the find_value function as follows:
function find_value($array,$value)
{
for($i=1;$i<sizeof($array);$i++)
{
if($array[$i] == $value)
{
return i$;
}
}
return FALSE;
}
If the function finds the value in the array, it returns the number of the array
element where it found $value. However, if it does not find the value anywhere
in the array, it returns FALSE.
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Using built-in functions
PHP’s built-in functions are one reason why PHP is so powerful and useful.
The functions included with PHP are normal functions. They are no different
than functions you create yourself. It’s just that PHP has already done all the
work for you.
Rather than discussing built-in functions here, out of context, I discuss specific
PHP functions where I describe tasks in which functions can be very
helpful. For example, in Chapter 7, I discuss several functions that can be
used to check whether a variable exists or whether it is empty. Here are a
couple of those functions:
isset($varname)
empty($varname)
Also, in Chapter 5 I describe several functions that are useful for formatting
and manipulating numbers and strings. And other PHP built-in functions are
discussed throughout the book.
Appendix B is a reference list of many useful functions. Keep this list handy
when writing scripts so you can quickly look up PHP built-in functions. Although
you could write functions yourself to perform the tasks, take advantage of
PHP’s functions whenever possible. The reference in Appendix B does not
include all the functions, of course — there are hundreds — but it includes
the functions I have found to be most useful. All the functions are listed and
described in the PHP documentation on the PHP Web site at
www.php.net/docs.php.
Handling Errors
Sometimes functions fail. Sad, but true. You write them to carefully handle all
possibilities, but something can still go wrong. For example, a function that
connects to a database might fail because the database is currently down.
It’s not the function’s fault; the situation is beyond its control. A well-written
function tries to anticipate all possible situations, but recognizes that the
unexpected can happen by including a statement that returns FALSE when
the function is unable to carry out its mission for unexpected reasons.
Your script should anticipate any possible function failure and handle the situation.
One possible action is to display your own message, rather than allow the
user to see the warning message provided by PHP. PHP provides the die statement,
which displays the message you specify. The format of the die statement
is as follows:
die(“message”);
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The die statement stops the script and prints out whatever you have entered
in the place of message. When you use it with a function, you use it with or,
as follows:
functionname() or die(“message”);
If the function returns FALSE, the die statement stops the script and prints
out the message.
For example, if you use a function to connect to a MySQL database, you could
use the following statement:
mysql_connect(“host”,”user”,”password”)
or die(“Database is not available. Try again later.”);
Remember, if the function fails, PHP will display a warning message. If you
want your message to be displayed instead of the PHP warning message,
you need to change your error-reporting level so that warning messages are
not displayed, or shut off the display of all error messages, as described in
Chapter 4. Otherwise, both the PHP warning and your message will be
displayed.
You can use die with any function, but it doesn’t make sense to use it when
FALSE is a legitimate return value. Remember, die stops the script dead in its
tracks.
You can also handle possible function failures by using the function call as a
condition. For example, you can get the same result as the previous example
by using the following statements instead:
if(!mysql_connect(“host”,”user”,”password”))
{
echo “Database is not available. Try again later\n”;
exit();
}
Notice the exclamation point before the function call, making it a negative
condition. The condition is TRUE if the function returns FALSE.
The exit statement does the same thing as the die statement. Keep in mind
that you can use any statement in the if block; you can even have the script
send you an e-mail if the database is unreachable.
175 Chapter 8: Reusing PHP Code
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Chapter 9
Object-Oriented Programming
Meets PHP
In This Chapter
Understanding object-oriented programming
Identifying objects
Writing classes
Using classes
PHP began life as a simple set of scripts. Over the course of its life, PHP
has added some object-oriented programming features, and objectoriented
programming became possible with PHP 4. With the introduction of
PHP 5, the PHP developers have really beefed up the object-oriented features
of PHP, resulting in both more speed and added features. Much of this
improvement is invisible — changes introduced with the Zend 2 engine that
powers PHP 5, that make scripts using objects run much faster and more
efficiently than they did in PHP 4. In addition, to speeding up scripts, objectoriented
functionality has been added to PHP that object-oriented programmers
have been waiting for.
Introducing Object-Oriented
Programming
Object-oriented programming is an approach to programming that uses objects
and classes, which are discussed in more detail later in this chapter. Objectoriented
programming is widespread today, and many universities teach
object-oriented programming in beginning programming classes. Currently,
Java and C++ are the most prevalent languages used for object-oriented
programming.
Object-oriented programming is not just a matter of using different syntax.
It’s a different way of analyzing programming problems. The program is
designed by modeling the programming problem. For example, a programmer
designing a program to support a company’s sales department may look at
the programming problem in terms of the relationships between customers
and sales and credit lines — in other words, in terms of the design of the
sales department itself.
In object-oriented programming, the elements of a program are objects. The
objects represent the elements of the problem your program is meant to
solve. For example, if the program is related to a used-car lot, the objects are
probably cars and customers. Or if the program is related to outer space, the
objects would probably be stars and planets.
Object-oriented programming developed new concepts and new terminology
to represent those concepts. Understanding the terminology is the road to
understanding object-oriented programming.
Objects and classes
The basic elements of object-oriented programs are objects. It’s easiest to
understand objects as physical objects. For example, a car is an object. A car
has properties, such as color, model, engine, and tires, also called attributes.
A car has things it can do, too, such as move forward, move backward, park,
roll over, and play dead (well, mine does anyway).
In general, objects are nouns. A person is an object. So are animals, houses,
offices, customers, garbage cans, coats, clouds, planets, and buttons. However,
objects are not just physical objects. Often objects, like nouns, are more conceptual.
For example, a bank account is not something you can hold in your
hand, but it can be considered an object. So can a computer account. Or a
mortgage. A file is often an object. So is a database. Orders, e-mail messages,
addresses, songs, TV shows, meetings, and dates can all be objects.
A class is the script that serves as the template, or the pattern, that is used to
create an object. The class defines the properties, the attributes, of the
object. It also defines the things the object can do — its responsibilities. For
example, you write a class that defines a car as four wheels and an engine
and lists the things it can do, such as move forward and park. Then, given
that class, you can write a statement that creates a car object. Your new car
is created following the pattern in your class. When you use your car object,
you may find that it is missing a few important things, like a door or a steering
wheel or a reverse gear. That’s because you left those out of the class
when you wrote it.
As the person who writes a class, you know how things work inside the class.
But it’s not necessary to know how an object accomplishes its responsibilities
in order to use it; anyone can use a class. I have no clue how a telephone
178 Part III: Basic PHP Programming
object works, but I can use it to make a phone call. The person who built the
telephone knows what’s happening inside it. When there’s new technology,
the phone builder can open my phone and improve it. As long as he doesn’t
change the interface — the keypad and buttons — it doesn’t affect my use of
the phone at all.
Properties
Objects have properties, also sometimes called attributes. A car may be red,
green, or covered in polka dots. Properties — such as color, size, or model
for a car — are stored inside the object. Properties are set up in the class as
variables. For example, the color attribute is stored in the object in a variable,
given the descriptive name such as $color. Thus, the car object may
contain $color = red.
The variables that store properties can have default values, can be given
values when the object is created, or values can be added or modified later.
For example, a car is created red, but when it is painted later, $color is
changed to chartreuse.
Methods
The things objects can do are sometimes referred to as responsibilities. For
example, a car object can move forward, stop, backup, and park. Each thing
an object can do — each responsibility — is programmed into the class and
called a method.
In PHP, methods use the same syntax as functions. Although the code looks
like the code for a function, the distinction is that methods are inside a class.
It can’t be called independently of an object. PHP won’t allow it. This type of
function can perform its task only when called with an object.
When creating methods, give them names that are descriptive of what they
do. Methods often have names like parkCar or getColor. Methods, like
other PHP entities, can be named with any valid name, but are often named
with camel caps, by convention.
The methods are the interface between the object and the rest of the world.
The object needs methods for all its responsibilities. Objects should interact
with the outside world only through their methods. If your neighbor object
wants to borrow a cup of sugar, you want him to knock on your door and
request the sugar. You don’t want him to just climb in the kitchen window and
help himself. Your house object should have a front door, and neighbor
objects should not be able to get into your house without using the front
door. In other words, your house object has a method for openFrontDoor that
179 Chapter 9: Object-Oriented Programming Meets PHP
the neighbor must use. There should not be any other way the neighbor can
get into the house. Opening the front door is something your house object
can do, via a method called openDoor. Don’t leave any open windows in your
object design.
A good object should contain all it needs to perform its responsibilities, but
not a lot of extraneous data. It should not perform actions that are another
object’s responsibility. The car object should travel and should have everything
it needs to perform its responsibilities, such as gas, oil, tires, engine,
and so on. The car object should not cook and does not need to have salt or
frying pans. Nor should the cook object carry the kids to soccer practice.
Inheritance
Objects should contain only the properties and methods they need. No more.
No less. One way to accomplish that is to share properties and methods
between classes by using inheritance. For example, suppose you have two
rose objects: one with white roses and one with red roses. You could write
two classes: a redRose class and a whiteRose class. However, a lot of the
information is the same for both objects. Both are bushes, both are thorny,
and both bloom in June. Inheritance enables you to eliminate the duplication.
You can write one class called Rose. You can store the common information
in this class, such as $plant = bush, $stem=thorns, and $blooms=June.
Then you can write subclasses for the two rose types. The Rose class is
called the master class or the parent class. redRose and whiteRose are the
subclasses, which are referred to as child classes, or the kids, as my favorite
professor fondly referred to them.
Child classes inherit all the properties and methods from the parent class. But
they can also have their own individual properties, such as $color=white for
the whiteRose class and $color=red for the redRose class.
A child class can contain a method with the same name as a method in a
parent class. In that case, the method in the child class takes precedence for
a child object. You can specify the method in the parent class for a child
object if you want, but if you don’t, the child class method is used.
Object-oriented concepts PHP 5 omits
If you’re familiar with object-oriented programming in other languages, you
may find that some features you’re accustomed to using aren’t available in
PHP. Things are getting better — many of the features missing in PHP 4 have
been added in PHP 5. The still-missing features include the following:
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Polymorphism: PHP does not allow more than one method, even a constructor,
to have the same name in a class. Therefore, you can’t implement
polymorphism as you’re used to doing. You can’t have two or more
methods with the same name in the same class that accept different
types or number of variables. Some people use switches and other mechanisms
to implement the functionality of polymorphism.
Multiple inheritance: PHP does not allow multiple inheritance. A class
can inherit from only one parent class.
Developing an Object-Oriented Program
Object-oriented programs require a lot of planning, even more than procedural
programs that process statement from beginning to end, without using classes.
You need to plan your objects and their properties and what they can do. Your
objects need to cover all their responsibilities without encroaching on the
responsibilities of other objects. For complicated projects, you may have to do
some model building and testing before you can feel reasonably confident that
your project plan includes all the objects it needs.
Choosing objects
Your first task is to develop the list of objects needed for your programming
project. If you’re working alone and your project is small, the objects may be
obvious. However, if you’re working on a large, complex project, selecting the
list of objects can be more difficult. For example, if your project is developing
the software for a bank, your list of possible objects is large: account, teller,
money, checkbook, wastebasket, guard, vault, alarm system, customer, loan,
interest, and so on. But, do you need all those objects? What is your program
going to do with the wastebasket in the front lobby? Or the guard? Well, perhaps
your program needs to schedule shifts for the guards.
One strategy for identifying your objects is to list all the objects you can think
of — that is, all the nouns that may have anything to do with your project.
Sometimes programmers can take all the nouns out of the project proposal
documentation to develop a pretty comprehensive list of possible objects.
After you have a long list of possible objects, your next task is to cross off
as many as possible. You should eliminate any duplicates, objects that have
overlapping responsibilities and objects that are unrelated to your project.
For example, if your project relates to building a car, your car project probably
needs to have objects for every part in the car. On the other hand, if your
project involves traffic control in a parking garage, you probably only need a
car object that you can move around; the car’s parts don’t matter for this
project.
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Selecting properties and
methods for each object
After you have a comprehensive list of objects, you can begin to develop the
list of properties for each object. Ask yourself what you need to know about
each object. For example, for your car repair project, you probably need to
know things like when the car was last serviced, its repair history, any accidents,
details about the parts, and so on. For your parking garage project,
you probably need to know only the car’s size. How much room does the car
take up in the parking garage?
You need to define the responsibilities of each object, and each object needs
to be independent. It needs methods for actions that handle all of its responsibilities.
For example, if one of your objects is a bank account, you need to
know what a bank account needs to do. Well, first, it needs to be created, so
you can define an openNewAccount method. It needs to accept deposits and
disburse withdrawals. It needs to keep track of the balance. It needs to report
the balance when asked. It may need to add interest to the account periodically.
Such activities come to mind quickly.
However, a little more thought, or perhaps testing, can reveal activities that
were overlooked. For example, the account stores information about its
owner, such as name and address. Did you remember to include a method to
update that information when the customer moves? It may seem trivial compared
to moving the money around, but it won’t seem trivial if you can’t do it.
Creating and using the class
After you have decided on the design of an object, you can create and then
use the object. The steps for creating and using an object are shown below:
1. Write the class statement.
The class statement is a PHP statement that is the blueprint for the
object. The class statement has a statement block that contains PHP
code for all the properties and methods that the object has.
2. Include the class in the script where you want to use the object.
The class statement can be written in the script itself. However, it is
more common to save the class statement in a separate file and use an
include statement to include the class at the beginning of the script
that needs to use the object.
3. Create an object in the script.
You use a PHP statement to create an object based on the class. This is
called instantiation.
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4. Use the new object.
After you create a new object, you can use it to perform actions. You can
use any method that is inside the class statement block.
The rest of this chapter provides the details needed to complete these steps.
Defining a Class
After you’ve determined the objects, properties, and methods your project
requires, you’re ready to define classes. The class is the template (pattern)
for the object.
Writing a class statement
You write the class statement to define the properties and methods for the
class. The class statement has the following general format:
class className
{
Add statements that define the properties
Add all the methods
}
You can use any valid PHP identifier for the class name, except the name
stdClass. PHP uses the name stdClass internally, so you can’t use this
name.
All the property settings and method definitions are enclosed in the opening
and closing curly brackets. If you want a class to be a subclass that inherits
properties and methods, use a statement similar to the following:
class whiteRose extends Rose
{
Add the property statements
Add the methods
}
The object created from this class has access to all the properties and
methods of both the whiteRose class and the Rose class. The Rose class,
however, does not have access to properties or methods in the child class,
whiteRose. Imagine, the child owns everything the parent owns, but the
parent owns nothing of the child’s. What an idea.
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The next few sections show you how to set properties, and define methods,
within the class statement. For a more comprehensive example of a complete
class statement, see the section, “Putting it all together,” later in this
chapter.
Setting properties
When you’re defining a class, you declare all the properties in the top of the
class, as follows:
class Car
{
var $color;
var $tires;
var $gas;
Method statements
}
PHP does not require you to declare variables. In the other PHP scripts discussed
in this book, variables are not declared; they’re just used. You can do
the same thing in a class. However, it’s much better to declare the properties
in a class. By including declarations, classes are much easier to understand.
It’s poor programming practice to leave this out.
If you want to set default values for the properties, you can, but the values
allowed are restricted. You can declare a simple value, but not a computed
one, as detailed in the following examples:
The following variable declarations are allowed as default values:
var $color = “black”;
var $gas = 10;
var $tires = 4;
The following variable declarations are not allowed as default values:
var $color = “blue”.” black”;
var $gas = 10-3;
var $tires = 2*2;
An array is allowed in the variable declaration, as long as the values are
simple, as follows:
var $doors = array(“front”,”back”);
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You can set or change a variable’s value when you create an object, by using
the constructor (described in “Writing the constructor,” later in this chapter)
or a method you write for this purpose.
Using $this
Inside a class, $this is a special variable that refers to the properties of the
same class. $this can’t be used outside of a class. It’s designed to be used in
statements inside a class to access variables inside the same class.
The format for using $this is the following:
$this->varname
For example, in the Car class that has an attribute $gas, you would access
$gas in the following way:
$this->gas
Using $this refers to $gas inside the class. You can use $this in any of the
following statements as shown:
$this->gas = 20;
if($this->gas > 10)
$product[$this->size] = $price
As you can see, you use $this->varname in all the same ways you would use
$varname.
Notice that a dollar sign ($) appears before this but not before gas. Don’t
use a dollar sign before gas — as in $this->$gas — because it changes your
statement’s meaning. You may or may not get an error message, but it isn’t
referring to the variable $gas inside the current class.
Adding methods
Methods define what an object can do and are written in the class by using
the function format. For example, your car may need a method that puts gas
in the gas tank. You can have a variable called gas that contains the amount
of gas currently in the gas tank. You can write a method that adds an amount
of gas to $gas. You could add such a method to your class as follows:
185 Chapter 9: Object-Oriented Programming Meets PHP
class Car
{
var $gas = 0;
function addGas($amount)
{
$this->gas = $this->gas + $amount;
echo “$amount gallons added to gas tank”;
}
}
This looks just like any other function, but it’s a method because it’s inside a
class.
PHP provides some special methods with names that begin with __ (two
underscores). These methods are handled differently by PHP internally.
This chapter discusses three of these methods: construct, destruct, and
clone. Don’t begin the names of any of your own methods with two underscores
unless you are taking advantage of a PHP special method.
Writing the constructor
The constructor is a special method that is executed when an object is created
using the class as a pattern. A constructor is not required, and you don’t need
to use a constructor if you don’t want to set any property values or perform
any actions when the object is created. Only one constructor is allowed.
The constructor has a special name so that PHP knows to execute the
method when an object is created. Constructors are named __construct.
(Note the two underscores.) A constructor method looks similar to the
following:
function __construct()
{
$this->gas = 10; # starts with a full gas tank
$this->openDoor();
}
This constructor defines the new car. When the car is created, it has a full gas
tank and an open door.
Prior to PHP 5, constructors had the same name as the class. You may run
across classes written in this older style. PHP 5 looks first for a method called
__construct() to use as the constructor. If it doesn’t find one, it looks for a
method that has the same name as the class and uses that method for the
constructor. Thus, older classes still run under PHP 5.
186 Part III: Basic PHP Programming
Putting it all together
Your class can have as few or as many properties and methods as it needs.
These methods can be very simple or very complicated, but the goal of
object-oriented programming is to make the methods as simple as is reasonable.
Rather than cram everything into one method, it’s better to have several
smaller methods and have one method call another.
The following is a simple class:
class MessageHandler
{
var $message = “No message”;
function __construct($message)
{
$this->message = $message;
}
function displayMessage()
{
echo $this->message.”\n”;
}
}
The class has one property — $message — that stores a message. The message
is stored in the constructor.
The class has one method — displayMessage. This is the only thing the
messageHandler object is able to do — echo the stored message.
Suppose you want to add a method that changes the message to lowercase
and then automatically displays the message. The best way to write that
expanded class is as follows:
class MessageHandler
{
var $message = “No message”;
function __construct($message)
{
$this->message = $message;
}
function displayMessage()
{
echo $this->message.”\n”;
}
function lowerCaseMessage()
{
$this->message = strtolower($this->message);
$this->displayMessage();
}
}
187 Chapter 9: Object-Oriented Programming Meets PHP
Note the lowerCaseMessage() method. Because the class already has
a method to display the message, this new method uses the existing
displayMessage() method rather than include the statements in the new
method. Any time you write a method and find yourself writing code that you
have already written elsewhere in a different method in the same class, you
need to redesign the methods. In general, you should not have any duplicate
code in the same class.
The Listing 9-1 example is a more complicated class that can be used to
create an HTML form. To simplify the example, the form contains only text
input fields.
Listing 9-1: A Script That Contains a Class for a Form Object
<?php
/* Class name: Form
* Description: A class that creates a simple HTML form
* containing only text input fields. The
* class has 3 methods.
*/
class Form
{
var $fields=array(); # contains field names and labels
var $processor; # name of program to process form
var $submit = “Submit Form”; # value for the submit button
var $Nfields = 0; # number of fields added to the form
/* Constructor: User passes in the name of the script where
* form data is to be sent ($processor) and the value to show
* on the submit button.
*/
function __construct($processor,$submit)
{
$this->processor = $processor;
$this->submit = $submit;
}
/* Display form function. Displays the form.
*/
function displayForm()
{
echo “<form action=’{$this->processor}’ method=’post’>”;
echo “<table width=’100%’>”;
for($j=1;$j<=sizeof($this->fields);$j++)
{
echo “<tr><td align=\”right\”>
{$this->fields[$j-1][‘label’]}: </td>\n”;
echo “<td>
<input type=’text’
name=’{$this->fields[$j-1][‘name’]}’>
</td></tr>\n”;
}
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echo “<tr><td colspan=2 align=’center’>
<input type=’submit’
value=’{$this->submit}’></td></tr>\n”;
echo “</table>”;
}
/* Function that adds a field to the form. The user needs to
* send the name of the field and a label to be displayed.
*/
function addField($name,$label)
{
$this->fields[$this->Nfields][‘name’] = $name;
$this->fields[$this->Nfields][‘label’] = $label;
$this->Nfields = $this->Nfields + 1;
}
}
?>
This class contains four properties and three methods. The properties are as
follows:
$fields: An array that holds the fields as they are added by the user.
The fields in the form are displayed from this array.
$processor: The name of the script that the form is sent to. This variable
is used in the action attribute when the form tag is displayed.
$submit: The text that the user wants displayed on the submit button.
This variable’s value is used when the submit button is displayed.
$Nfields: The number of fields that have been added to the form so far.
The methods in this class are as follows:
__construct: The constructor, which sets the values of $processor
and $submit from information passed in by the user.
addField: Adds the name and label for the field to the $fields array. If
the user added fields for first name and last name to the form, the array
may look as follows:
$fields[1][name]=first_name
$fields[1][label]=First Name
$fields[2][name]=last_name
$fields[2][label]=Last Name
and so on
displayForm: Displays the form. It echoes the HTML needed for the
form and uses the values from the stored variables for the name of the
field and the label that the user sees by the field.
The next section describes how to use a class, including the form class
shown in Listing 9-1.
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Using a Class
The class code needs to be in the script that uses the class. Most commonly,
the class is stored in a separate include file and is included in any script that
uses the class.
To use an object, you first create the object from the class. Then that object
can perform any methods that the class includes. Creating an object is called
instantiating the object. Just as you can use a pattern to create many similar
but individual dresses, you can use a class to create many similar but individual
objects. To create an object, use statements that have the following format:
$objectname = new classname(value,value,…);
$Joe = new Person(“male”);
$car_Joe = new Car(“red”);
$car_Sam = new Car(“green”);
$customer1 = new Customer(“Smith”,”Joe”,$custID);
The object is stored in the variable name, and the constructor method is
executed. You can then use any method in the class with statements of the
following format:
$Joe->goToWork();
$car_Joe->park(“illegal”);
$car_Sam->paintCar(“blue”);
$name = $customer1->getName();
Different objects created from the same class are independent individuals.
Sam’s car gets painted blue, but Joe’s car is still red. Joe gets a parking ticket,
but it doesn’t affect Sam.
The script shown in Listing 9-2 shows how to use the form class that was created
in the previous section and shown in Listing 9-1.
Listing 9-2: A Script That Creates a Form By Using the Form Class
<?php
/* Script name: buildForm
* Description: Uses the form to create a simple HTML form
*/
require_once(“form.inc”);
echo “<html><head><title>Phone form</title></head><body>”;
$phone_form = new Form(“process.php”,”Submit Phone”);
$phone_form->addField(“first_name”,”First Name”);
$phone_form->addField(“last_name”,”Last Name”);
$phone_form->addField(“phone”,”Phone”);
190 Part III: Basic PHP Programming
echo “<h3>Please fill out the following form:</h3>”;
$phone_form->displayForm();
echo “</body></html>”;
?>
First, the script included the file containing the class into the script. The
class is stored in the file form.inc. The script creates a new form object called
$phone_form. Three fields are added. The form is displayed. Notice that some
additional HTML code was output in this script. That HTML could have been
added to the displayForm method just as easily.
The script creates a form with three fields, using the form class. Figure 9-1
shows the resulting Web page.
Making Properties and Methods Private
Properties and methods can be public or private. Public means that methods
or properties inside the class can be accessed by the script that is using the
class or from another class. For example, the following class has a public
attribute and a public method as shown:
class Car
{
var $gas = 0;
function addGas($amount)
{
$this->gas = $this->gas + $amount;
echo “$amount gallons added to gas tank”;
}
}
Figure 9-1:
The form
displayed by
the script in
Listing 9-2.
191 Chapter 9: Object-Oriented Programming Meets PHP
The public attribute in this class can be accessed by a statement in the script
outside the class, as follows:
$mycar = new Car;
$gas_amount = $mycar->gas;
After these statements are run, $gas_amount contains the value stored in
$car inside the object. The attribute can also be modified from outside the
class, as follows:
$mycar->gas = 20;
Allowing script statements outside the class to directly access the properties
of an object is poor programming practice. All interaction between the object
and the script or other classes should take place using methods. The example
class has a method to add gas to the car. All gas should be added to the car
using the addGas method, which is also public, using statements similar to
the following:
$new_car = new Car;
$new_car->addGas(5);
You can prevent access to properties by making them private. PHP provides
two options for making properties and methods private, as follows:
private: No access from outside the class, either by the script or from
another class.
protected: No access from outside except from a class that is a child of
the class with the protected attribute or method.
You can make an attribute private as follows:
private $gas = 0;
With the attribute specified as private, a statement like the previous statement
that attempts to access the attribute directly gets the following error message:
Fatal error: Cannot access private property car::$gas in
c:\testclass.php on line 17
Now, the only way gas can be added to the car is using the addGas method.
Because the addGas method is part of the class statement, it can access the
private attribute.
In the same way, you can make methods private or protected. In this case,
you want the outside world to use the addGas method. However, you may
want to be sure that people buy the gas that is added. You don’t want any
stolen gas in your car. You could write the following class:
192 Part III: Basic PHP Programming
class Car
{
private $gas = 0;
private function addGas($amount)
{
$this->gas = $this->gas + $amount;
echo “$amount gallons added to gas tank”;
}
function buyGas($amount)
{
$this->addGas($amount);
}
}
With this class, the only way gas can be added to the car from the outside is
with the buyGas method. The buyGas method uses the addGas method to
add gas to the car, but the addGas method can’t be used outside the class
because it is private. If a statement outside the class attempts to use addGas,
as follows, a fatal error is displayed, as it was for the private attribute:
$new_car = new Car;
$new_car->addGas(5);
However, you can now add gas to the car using the buyGas method, as follows:
$new_car = new Car;
$new_car->buyGas(5);
You see the following output:
5 gallons added to gas tank
It’s good programming practice to hide as much of your class as possible.
Make all properties private. Only make methods public that absolutely need
to be public.
PHP also provides an option to make properties and methods public. Although
you don’t need to use the public option, because public is the default, it helps
to make the class more readable. The following statement:
public $gas = 0;
has the same effect as:
var $gas = 0;
193 Chapter 9: Object-Oriented Programming Meets PHP
Using Exceptions
PHP provides an error-handling class called Exception. You can use this class
to handle undesirable things that happen in your script. When the undesirable
thing that you define happens, a routine you have written is performed. In
object-oriented talk, this is called throwing an exception.
In the car class, you keep track of the gas in the car and stop the car when it
runs out of gas. You expect your program to detect 0 gallons and react. You
don’t expect the gas in the gas tank to be a negative amount. You consider
that to be an exception, and you want to be sure that won’t happen in your
script. To deal with this, you can write a routine that uses the Exception
class to watch for a negative gas amount. The following statements check for
this situation:
$this->gas = $this->gas – 5;
try
{
if ($this->gas < 0)
{
throw new Exception( “Negative amount of gas.”);
}
}
catch (Exception $e)
{
echo $e->getMessage();
echo “\n<br />\n”;
exit();
}
The preceding script contains a try block and a catch block:
In the try block, you test a condition. If the condition is TRUE, you throw
an exception — in other words, you create an Exception object. The
Exception object has a property that stores the message you sent when
you threw the exception.
In the catch block, you catch the exception and call it $e. Then you execute
the statements in the catch block. One of the statements is a call to
a method called getMessage in the Exception class. The getMessage
function returns the message that you stored, and your statement echoes
the returned message. The statements then echo the end-of-line characters
so the message is displayed correctly. The script stops on the exit
statement.
If no exception is thrown, the catch block has nothing to catch, and it is
ignored. The script proceeds to the statements after the catch block.
194 Part III: Basic PHP Programming
Copying Objects
PHP provides a method you can use to copy an object. The method is __clone,
with two underscores. You can write your own __clone method in a class if
you want to specify statements to run when the object is copied. If you don’t
write your own, PHP uses it’s default __clone method that copies all the
properties as is. The two underscores indicate that the clone method is a
different type of method, and thus is called differently, as shown in the following
example.
For example, you could write the following class:
class Car
{
private $gas = 0;
private $color = “red”;
function addGas($amount)
{
$this->gas = $this->gas + $amount;
echo “$amount gallons added to gas tank”;
}
function __clone()
{
$this->gas = 0;
}
}
Using this class, you could create an object and copy it as follows:
$firstCar = new Car;
$firstCar->addGas(10);
$secondCar=clone $firstCar;
After these statements, you have two cars:
$firstCar: This car is red and contains 10 gallons of gas. The 10 gallons
were added with the addGas method.
$secondCar: This car is red, but contains 0 gallons of gas. The duplicate
car is created using the __clone method in the Car class. This method
sets gas to 0 and doesn’t set $color at all.
If you did not have a __clone method in the Car class, PHP would use a default
__clone method that would copy all the properties, making $secondCar both
red and containing 10 gallons of gas.
195 Chapter 9: Object-Oriented Programming Meets PHP
Destroying Objects
You can destroy an object with the following statement:
unset($objName);
For example, you could create and destroy an object of the Car class with the
following statements:
$myCar = new Car;
unset($myCar);
After $myCar is unset, the object no longer exists at all.
PHP provides a method that is automatically run when an object is destroyed.
You add this method to your class and call it __destruct. For example, the
following class contains a __destruct method:
class Bridge
{
function __destruct()
{
echo “The bridge is destroyed”;
}
}
If you use the following statements, the object is created and destroyed:
$bigBridge = new Bridge;
unset($bigBridge);
The output from these statements is:
The bridge is destroyed
The output is echoed by the __destruct method when the object is unset.
The __destruct method is not required. It’s just available for you to use if
you want to execute some statements when the object is destroyed. For
example, you might want to close some files or copy some information to
your database.
196 Part III: Basic PHP Programming
Part IV
Common PHP
Applications
In this part . . .
Part IV shows how to apply the features and functionality
of PHP to common programming tasks. You find
out how to write scripts to do the tasks that programmers
most often need to do, and you also discover how PHP
can interact with databases, operating systems, and e-mail
applications. When you finish this part, you will know how
to write scripts by using HTML forms to interact with your
user, how to handle data, and many other tasks commonly
performed with PHP.
Chapter 10
The Basics of Web Applications
In This Chapter
Understanding Web site security
Displaying static pages
Collecting information from users with HTML forms
Processing information received from users
PHP was originally designed for Web programming, and although its use
for general-purpose scripts is growing, PHP is still used most frequently
to develop dynamic Web sites. Static Web pages — pages where all users see
the same Web page — don’t allow for interaction between the user and the
Web page. Dynamic Web pages, on the other hand, allow users to interact
with the Web page. Users may see different Web pages, based on information
they type into the Web page. For example, users might be required to type in
valid usernames and passwords before they can see any Web pages on the
Web site, allowing the site to customize Web pages based on users’ previous
preferences or profiles. Alternatively, users may select a type of product from
an online catalog and see only the Web pages containing products of the type
they select.
A dynamic Web page collects information from the user with an HTML form.
The information that the user types into the form is then processed, depending
on what the information will be used for. The information may be stored
(see Chapter 12 for more on storing data using PHP) or used in a conditional
statement to display alternative Web pages.
In this chapter, I do not tell you about the HTML required to display a form; I
assume you already know HTML. (If you don’t know HTML or need a refresher,
check out HTML 4 For Dummies, 4th Edition, by Ed Tittel and Natanya Pitts
[Wiley Publishing, Inc.].) What I do tell you is what you need to consider to
keep your Web site secure and how to use PHP to display HTML forms and to
process the information that users type into the form.
Securing Your Web Site
Web applications are particularly vulnerable to attacks from the outside.
Most Web sites are open to the public, offering services, products, or information
to anyone who visits. Dynamic Web sites are particularly vulnerable
because they accept information from visitors to the site. Although the vast
majority of visitors are good guys, trying to use the Web site for its intended
purpose, a few people out have intentions that are not so pure, including the
following groups:
People who want to steal things: These are the folks who hope to find a
file sitting around full of valid credit card numbers or a map to the pot of
gold at the end of the rainbow.
People who want to destroy your Web site: These saboteurs may think
it’s funny to wreck your site, or they may cause damage just to prove
how smart they are.
People who want to harm your users: These folks add things to your
Web site that harm or steal from the people who visit your site.
This is not a security book. Security is a large, complex issue, and I am not a
security expert. Nevertheless, I want to call a few issues to your attention and
make some suggestions to help you protect your Web site. The following measures
will increase the security of your Web site, but if your site handles really
important, secret information, read some security books and talk to some
experts:
Ensure the security of the computer that hosts your Web site. This is the
responsibility of the system administrator, which may or may not be you.
Keep information private. Don’t be more public than necessary. Store
your information so it can’t be easily accessed from the Web.
Be cautious of information from users. Always clean any information
that you didn’t generate yourself.
Use a secure Web server. This requires extra work, but it’s important if
you have top-secret information.
These topics are covered in more detail in the following sections.
Ensuring the security of the host computer
Your first line of defense is to make sure that the computer that hosts the Web
site is secure. The computer’s system administrator is responsible for keeping
unauthorized visitors and vandals out of the system. Security measures include
such things as firewalls, encryption, password shadowing, scan detectors, and
200 Part IV: Common PHP Applications
so on. In most cases, the system administrator is not you. If it is, you need to
do some serious investigation into security issues. If you’re using a Web hosting
company, you may want to discuss security with those folks, to reassure
yourself that they’re using sufficient security measures.
Keeping information private
Keep information as private as possible. Of course, the Web pages you want
visitors to see must be stored in your public Web space directory. However,
users don’t need to see the names of the files stored there. You may have
noticed that sometimes a site shows you a list of all the files in the directory.
This is generally not a good idea. Your Web site isn’t very secure if a visitor
can look at any file on your site.
This list of files is displayed when the URL that the visitor types in points at a
directory, rather than a specific file, and the directory doesn’t contain a file
with the default directory name. Most Web servers look first in a directory for
a default name, specified in the server configuration, often index.html. If the
directory doesn’t contain a file with this default name, the server may display
a list of files in the directory. A better choice is to have the Web server display
a message telling visitors that they can’t access the directory, similar to the
following message:
Forbidden
You don’t have permission to access /secretdirectory on this
server.
A setting in the configuration of the Web server determines whether users
see a list of files or a message. The Web server administrator can change the
behavior. For example, in Apache, you control what is displayed by using an
option called Indexes, which can be turned on or off in the httpd.conf file
as follows:
Options Indexes // turns file listing on
Options -Indexes // turns file listing off
See the documentation for your Web server to allow or not allow directory
listings in the user’s Web browser.
It’s also not wise to name a file an obvious, guessable name. For example, if
you have a file containing secret passwords, it’s not a good idea to name it
passwords.php. You may want to call the file something odd or boring, such
as vegetableRecipes.php. I know this suggestion violates other parts of
the book where I promote informative filenames, but this is a special case.
Malicious people sometimes do obvious things like typing www.yoursite.
com/passwords.html into their browsers to see what happens.
201 Chapter 10: The Basics of Web Applications
Not everything needs to be public. For example, your database should not be
stored in a public location. In fact, it can be stored on a totally different computer.
Also, as discussed in Chapter 8, include files can be stored in a separate
location, a space on the computer that can’t be accessed from the Web.
Being cautious of information from users
Users can enter dangerous information into forms, either accidentally or with
malicious intent. Therefore, never store or use information from forms without
checking it first. Check it for reasonable formats and dangerous characters.
Even characters entered accidentally can sometimes cause problems in your
database or scripts. In particular, you don’t want to accept HTML tags — such
as <script> tags — from forms. Using script tags, a user can enter an actual
script, perhaps a malicious one. If you accept the form field without checking
it and store it in your database, you could have any number of problems, particularly
if the stored script was sent in a Web page to a visitor to your Web
site. For more on checking data from forms, see the section “Checking the
information” later in this chapter.
Using a secure Web server
Communication between your Web site and its visitors is not totally secure.
When the files on your Web site are sent to the user’s browser, it is possible
for someone on the Internet between you and the user to read the contents of
these files as they pass by. For most Web sites, this isn’t an issue, but if your
site collects or sends credit card numbers or other secret information, use a
secure Web server to protect this data.
Secure Web servers use SSL (Secure Sockets Layer) to protect communication
sent to and received from browsers. This is similar to the scrambled telephone
calls you hear about in spy movies. The information is encrypted (translated
into coded strings) before it is sent across the Web. The receiving software
decrypts it into its original content. In addition, your Web site uses a certificate
that verifies your identity. Using a secure Web server is extra work, but
it’s necessary for some applications.
You can tell when you’re communicating using SSL because the URL begins
with https rather than http.
Information about secure Web servers is specific to the Web server you’re
using. To find out more about using SSL, look at the Web site for the Web server
you’re using. For example, if you’re using Apache, check out two open source
projects that implement SSL for Apache at www.modssl.org and www.apachessl.
org. Commercial software is also available that provides a secure server
202 Part IV: Common PHP Applications
based on the Apache Web server. If you’re using Microsoft IIS, search for SSL
on the Microsoft Web site at www.microsoft.com.
Displaying Static Web Pages
The simplest Web page design is a static Web page. If you need only static Web
pages on your Web site, you don’t need PHP. However, you may need static
Web pages interspersed with your dynamic pages.
PHP can be used to display any Web pages, including static pages. You simply
use echo statements to echo the appropriate HTML. If you have a Web page
containing only HTML that needs to be displayed in a PHP script, the most
efficient way to display the static Web page is to include it where it’s needed
with the following statement:
include(“filename”);
If you need to turn an existing static Web page into a PHP script, for some
unlikely reason, you can add PHP tags at the beginning and end of the file.
Then add echo at the top of the file and enclose the existing HTML code in
single quotes.
Working with HTML Forms
For a Web page to be interactive, it must collect information from the user,
which is done with HTML forms. The information collected may simply be a
username and password for a user login. A form can also be long and elaborate,
collecting a great deal of information from a user, such as shipping and
credit card information for an online purchase application or a survey form
asking many questions for research purposes.
To use HTML forms to collect information, your script displays the form on
the Web site, and the user types information into text fields or selects items
from a list. The user then clicks a button to submit the form information. When
the form is submitted, the information in the form is passed to a second separate
script, which processes the information.
This chapter provides basic information on using forms in a dynamic Web site.
Often the information collected is stored in a database, or the form is displayed
by using information retrieved from a database. If you’re planning to use HTML
forms teamed with a MySQL database, you can find more detailed information
and more complex solutions in PHP & MySQL For Dummies by yours truly
(Wiley Publishing, Inc.).
203 Chapter 10: The Basics of Web Applications
Collecting information
from Web site visitors
HTML forms are used to collect information from Web site visitors. If you’re
unfamiliar with HTML forms, check out HTML 4 For Dummies, 4th Edition, by
Ed Tittel and Natanya Pitts.
Displaying HTML Forms
To display a form by using PHP, you can do one of the following:
Use echo statements to echo the HTML for a form. The following statements
echo a form by using this method:
echo “<form action=’processform.php’ method=’POST’>\n
<input type=’text’ name=’name’>\n
<input type=’submit’ value=’Submit Name’>\n
</form>\n”;
Use plain HTML outside the PHP sections. For a plain static form, you
don’t need to include it in a PHP section. For example, the following
statements produce the same form as the preceding example:
<?php
statements in PHP section
?>
<form action=”processform.php” method=”POST”>
<input type=”text” name=”fullname”>
<input type=”submit” value=”Submit Name”>
</form>
<?php
statements in PHP section
?>
Both of these examples display the same form, which is shown in Figure 10-1.
Figure 10-1:
A form
produced
by HTML
statements.
204 Part IV: Common PHP Applications
The form in Figure 10-1 has one text field, which is blank. It also has a button
labeled Submit Name. The user types a name into the text field and clicks the
button. When the user submits the form, the information in the form is passed
to the script designated in the action attribute of the form tag. In this example,
the action attribute is action=”processform.php”, so when the user clicks
the submit button, the script processform.php is called, and the information
in the form is passed to it. (I am using processform.php as an example name
here. You can name the script that processes the form with any name you
want.)
PHP allows you to use variables in PHP forms, making the forms more powerful.
Using variables, you can display information in the input text fields and
build dynamic lists for selection boxes, radio buttons, and check boxes.
Displaying information in text fields
In some cases, you may want to display information in the text fields rather
than just display blank fields. For example, you may want to display a default
value in a field. Or, when displaying a form to a user to reenter incorrect
information, you want to retain the correct information so that the user has
to retype information only in the field with the error.
To display text fields that contain information, you use the following format
for the input field HTML statements:
<input type=”text” name=”fieldname” value=”content”>
For example, suppose you’re displaying a form to collect a customer’s name
and address. You know that most of your customers live in the U.S., so you
decide to display the field with US as the default. If customers are from the
U.S., you save them some typing and avoid errors they may type in. If customers
are not from the U.S., they can just replace US with the correct country.
You can display the country field with the following statement:
<input type=”text” name=”country” value=”US”>
In some cases, you may want to display variable information in a text field.
You can use a PHP variable to display information. For example, suppose you
have customer information (such as a phone number) stored in a database,
and you want to display the information in a form so that the user can update
any incorrect or outdated information. First, you retrieve the customer information
from a database (see Chapter 12 for the lowdown on using a database)
and store the information in variables. Next, you can display the form by using
the information in the variables in one of two ways. You can create an input
field in an HTML section by using a short PHP section for the value only, as
follows:
<input type=”text” name=”phone” value=”<?php echo $phone ?>”>
205 Chapter 10: The Basics of Web Applications
Alternatively, you can create an input field by using an echo statement inside
a PHP section:
echo “<input type=’text’ name=’phone’ value=’$phone’>”;
If you’re using a long form with only an occasional variable, it’s more efficient
to use the first format. If your form uses many variables, it’s more efficient to
use the second format.
The script in Listing 10-1 displays a form containing customer information.
Figure 10-2 shows the output from this script.
Listing 10-1: A Script That Displays an HTML Form
<?php
/* Script name: displayForm
* Description: Script displays a form and populates the
* form fields with the values of an array.
*/
echo “<html>
<head><title>Customer Address</title></head>
<body>”;
$customer = array( “firstName”=>”John”,
“midName”=>”Jay”,
“lastName”=>”Smith”,
“street”=>”1234 Oak St.”,
“city”=>”Smalltown”,
“state”=>”ID”,
“zip”=>”88888”);
Figure 10-2:
A form
showing a
customer’s
address.
206 Part IV: Common PHP Applications
$labels = array( “firstName”=>”First Name:”,
“midName”=>”Middle Name:”,
“lastName”=>”Last Name:”,
“street”=>”Street Address:”,
“city”=>”City:”,
“state”=>”State:”,
“zip”=>”Zipcode:”);
echo “<h2 align=’center’>Address for
{$customer[‘firstName’]}
{$customer[‘midName’]}
{$customer[‘lastName’]}</h2>\n”;
echo “<p align=’center’>
<b>Please check the information below and change any
information that is incorrect.</b>
<hr>
<form action=’processform.php’ method=’POST’>
<table width=’95%’ border=’0’ cellspacing=’0’
cellpadding=’2’>\n”;
foreach($customer as $field=>$value)
{
echo “<tr>
<td align=’right’> <B>{$labels[$field]} </br></td>
<td><input type=’text’ name=’$field’ size=’65’
maxlength=’65’ value=’{$customer[$field]}’></td>
</tr>”;
}
echo “</table>
<div align=’center’><p><input type=’submit’
value=’Submit Address’> </p></div>
</form>”;
?>
</body></html>
Notice the following in displayForm.php, shown in Listing 10-1:
An array is created at the start of the script, which contains the information
that is displayed in the form. In real-life applications, you probably
obtain this information from a database, a file, or other sources.
An array is created that contains the labels that are used in the form.
The script processform.php is named as the script that runs when the
form is submitted. The information in the form is sent to processform.
php, which processes the information.
The form is formatted with an HTML table. Tables are an important
part of HTML. If you’re not familiar with HTML tables, check out HTML 4
For Dummies, 4th Edition, by Ed Tittel and Natanya Pitts.
The script loops through the $customer array with a foreach statement.
The HTML code for a table row is output in each loop. The appropriate
array values are used in the HTML code.
207 Chapter 10: The Basics of Web Applications
For security reasons, always include maxlength — which defines the number
of characters users are allowed to type into the field — in your HTML statement.
Limiting the number of characters helps prevent the bad guys from
typing malicious code into your form fields. If the information will be stored
in a database, set maxlength to the same number as the width of the column
in the database table.
Adding selection lists, radio buttons, and check boxes to forms
Other elements in HTML forms, such as selection lists, radio buttons, and
check boxes, can be used with variables. To use one of these elements in your
form, you echo the HTML that creates the form element and use variables for
information that changes. For example, you can use a selection list in your
form with the following statements:
echo “<select name=’dinner’ >
<option>$dinner1</option>
<option>$dinner2</option>
</select>”;
The selections in this selection list are the values in the variables. For example,
$dinner1 could display chicken, and $dinner2 could display fish. When
the user submits the form, the selected value is passed to the next script.
Similarly, you can use radio buttons in your form, as follows:
echo “<input type=’radio’ name=’dinner’
value=’$dinner1’>$dinner1
<input type=’radio’ name=’dinner’
value=’$dinner2’>$dinner2”;
The radio buttons that users can select are chicken and fish.
Check boxes allow users to check more than one box. Therefore, when you
use check boxes, the name attribute must be an array, as in the following
example:
echo “<input type=’checkbox’ name=’dinner[]’
value=’$dinner1’>$dinner1
<input type=’checkbox’ name=’dinner[]’
value=’$dinner2’>$dinner2”;
The form stores all the checked boxes in an array called $dinner. If both of the
values above are selected, the form stores both values in the array as follows:
$dinner[0]=chicken
$dinner[1]=fish
The script in Listing 10-2 displays a Web page with a selection list that allows
the user to select a date. In this form, the current date is selected by default.
208 Part IV: Common PHP Applications
Listing 10-2: A Script That Displays a Date Selection List
<?php
/* Script name: displayDate
* Description: Script displays a selection list, with
* three parts–months, days, and years. The
* current date is selected by default.
*/
echo “<html>
<head><title>Date</title></head>
<body>”;
/* Create an array of month numbers and names */
$monthName = array(1=> “January”, “February”, “March”,
“April”, “May”, “June”, “July”,
“August”, “September”, “October”,
“November”, “December”);
$today = Time(); #stores today’s date
echo “<div align=’center’><b>Select a date:</b>
<form action=’processform.php’ method=’POST’>\n”;
/* Build selection list for month */
$todayMO = date(“m”,$today); #get the month from $today
echo “<select name=’dateMO’>\n”;
for ($n=1;$n<=12;$n++)
{
echo “<option value=$n”;
if ($todayMO == $n) #adds selected attribute if today
{
echo “ selected”;
}
echo “> $monthName[$n]\n”;
}
echo “</select>”;
/* build selection list for the day */
$todayDay= date(“d”,$today); #get the day from $today
echo “<select name=’dateDay’>\n”;
for ($n=1;$n<=31;$n++)
{
echo “ <option value=$n”;
if ($todayDay == $n )
{
echo “ selected”;
}
echo “> $n\n”;
}
echo “</select>\n”;
/* build selection list for the year */
$startYr = date(“Y”, $today); #get the year from $today
echo “<select name=’dateYr’>\n”;
for ($n=$startYr;$n<=$startYr+3;$n++)
(continued)
209 Chapter 10: The Basics of Web Applications
Listing 10-2 (continued)
{
echo “ <option value=$n”;
if ($startYr == $n )
{
echo “ selected”;
}
echo “> $n\n”;
}
echo “</select>\n”;
echo “</form>\n”;
?>
</body>
</html>
The script creates $monthName, an array with elements that have all the
month numbers for keys and month names for values. Next it stores today’s
date in $today.
The rest of the script echoes a form that contains three selection lists, in drop
down boxes, for the three parts of the date: month, day, and year. For the
month, the foreach list creates a list of all the months, taken from the array
$monthName. Each month is compared with the month of today’s date stored
in $today. If the month is the same as today’s month, then the “selected”
attribute is added to the selection, so the month is the default selection.
Similar lists are created for day and year. These lists are just numbers, so a for
loop is used to create the list of numbers for the selection list. Again, each day
and year are compared to the day and year in today’s date and the current
day and year are selected as the default.
The form displayed by the script in Listing 10-2 is shown in Figure 10-3.
Figure 10-3:
A form that
allows a
user to
select
a date.
210 Part IV: Common PHP Applications
Receiving the information
In the form tag, you tell PHP which script to run when the user clicks the
submit button. You do this with the attribute action=”scriptname” in the
form tag. For example, in Listings 10-1 and 10-2 earlier in this chapter, I use
action=”processform.php”. When the user clicks the submit button, the
script runs and receives the information from the form.
The form data is available in the processing script in the PHP built-in arrays,
as described in Chapter 6. Information from forms that use the POST method
is available in the built-in array called $_POST. If your form uses the GET
method, the information is available in the array $_GET. Both types of form
information are also stored in an array called $_REQUEST. Each array index is
the name of the input field in the form. You get information from the array by
using the form field name as the array key. For example, suppose that you
echo the following field in your form that uses the POST method:
echo “<input type=’text’ name=’firstName’>”;
Setting name to firstName allows the processing script to use the variable
$_POST[‘firstName’], which contains the text the user typed into the field.
The information the user selects from selection drop-down lists or radio buttons
is similarly available for use. Because the user can check more than one
check box, information in check boxes is an array in the $_POST array and
available as a multidimensional array. For example, if two check boxes for
dinner choices (as described in the previous section) are both checked and
submitted, the information is available in the following array:
$_POST[‘dinner’][0] = chicken
$_POST[‘dinner’][1] = fish
The script in Listing 10-3 displays the values for all the fields in a form displayed
in Figure 10-2 earlier in the chapter.
Listing 10-3: A Script That Displays All the Fields from a Form
<?php
/* Script name: displayFormFields
* Description: Script displays all the information passed
* from a form.
*/
echo “<html>
<head><title>Customer Address</title></head>
<body>”;
foreach ($_POST as $field => $value)
{
echo “$field = $value<br>”;
}
?>
</body></html>
211 Chapter 10: The Basics of Web Applications
You can use this script to process the information from the form displayed
in Figure 10-2, which displays a customer’s address. To do so, you must use
the action attribute action=”displayFormFields.php” in the script
displayForm.php, which is shown in Listing 10-1. Then when the user clicks
the Submit Address button in the form, the script in Listing 10-3 runs and produces
the following output on a new Web page:
firstName = John
lastName = Smith
street = 1234 Oak St.
city = Smalltown
state = ID
zip = 88888
The script shown in Listing 10-3 displays all the values passed via the form in
Figure 10-2. In most cases, you don’t want to just display the values. Usually,
you want to use the values for a purpose. Either you use the values in a conditional
statement or you store the values, usually in a database.
212 Part IV: Common PHP Applications
POST versus GET
You use one of two methods to submit form
information. The methods pass the form data
differently and have different advantages and
disadvantages:
GET method: The form data is passed by
adding it to the URL that calls the formprocessing
script. For example, the URL may
look like this:
processform.php?lname=Smith&fname=Gol
iath
The advantages of this method are simplicity
and speed. The disadvantages are that
less data can be passed and the information
is displayed in the browser, which can
be a security problem in some situations.
POST method: The form data is passed as a
package in a separate communication with
the processing script.
The advantages of this method are unlimited
information passing and security of the
data. The disadvantages are the additional
overhead and slower speed.
For CGI programs other than PHP, the program
that processes the form must find the information
and put the data into variables. In this case,
the GET method is much simpler and easier to
use. Many programmers use the GET method
for this reason. However, PHP does all this work
for you. The GET and POST methods are equally
easy to use in PHP scripts. Therefore, when
using PHP, it’s almost always better to use the
POST method, because you have the advantages
of the POST method (unlimited data passing,
better security) without its main disadvantage
(more difficult to use).
Checking the information
Before you use the values in your script, you need to check the variables to
make sure they contain what you expect them to contain. The user may have
left required fields blank when entering information. The user may have made
mistakes in typing information, so the information makes no sense. Or, the user
may even have typed in malicious information that can cause problems for
you or for visitors using your Web site. Thus, never trust information received
from outside sources. Always check any information received in a form.
Validating information
Checking the information is called validating the information and includes
checking for empty fields and checking the format of the information, as
described in the following list:
Checking for empty fields: You can require users to enter information
in a field. If the field is blank, the user is told that the information is
required, and the form is displayed again so the user can type the missing
information.
Checking the format of the information: Whenever users must type
information in a form, you can expect a certain number of typos. You
can detect some of these errors when the form is submitted and then
point out errors to users and request that they type the information
again. For example, ab3&*xx is clearly not a valid zip code.
You can check for empty fields by using the following function:
empty($_POST[‘fieldname’])
For example, you could use the following code in your processing script:
if(empty($_POST[‘fieldname’]))
{
echo “Field is blank”;
statements that redisplay the field
}
Checking the format of information passed into a form can help identify typos.
For example, if the user types 8899776 in the zip code field, you know this is
not a valid zip code. This information is too long to be a zip code and too short
to be a zip + 4 code.
213 Chapter 10: The Basics of Web Applications
Checking the format also helps protect you from malicious users — users
who want to damage your Web site or your database or steal information
from you or your users. For example, you don’t want users to enter HTML
tags into a form field, something that can have unexpected results when sent
to a browser. (A script tag that allows a user to enter a script into a form field
is a particularly dangerous tag.)
If you check each field for its expected format, you can catch typos and prevent
most malicious content. However, checking information is a balancing
act. You want to catch as much incorrect data as possible, but you don’t want
to block legitimate information. For example, when you’re checking a phone
number, you limit it to numbers. The problem with this check is that it would
screen out legitimate phone numbers in the form such as 555-5555 or (888)
555-5555. So, you also need to allow hyphens parentheses, and spaces. You
could limit the field to a length of 14 characters, including parentheses, spaces,
and hyphens, but this screens out overseas numbers or numbers that include
an extension. The bottom line: You need to think carefully about what information
you want to accept or screen out for any field.
Using regular expressions to check user input
You can check field information by using regular expressions, which are
described in Chapter 7. You compare the information in the field to a pattern
to see if it matches. If it does not match, you have determined that the information
in the field is incorrect, and you can ask the user to reenter it.
For example, suppose you want to check an input field that contains the user’s
last name. You can expect names to contain letters, not numbers, and possibly
apostrophes (O’Hara), hyphens (Smith-Jones), and spaces (Van Dyke). Also,
it’s difficult to imagine a name longer than 50 characters. Thus, you can use
the following statements to check a name:
$last_name = trim($_POST[‘last_name’]);
if ( !ereg(“[A-Za-z’ -]{1,50}”,$last_name)
{
do stuff to require user to reenter last name;
}
First, use the trim function to remove any beginning or trailing blank spaces —
they’re not needed. Notice that the condition in the if statement is negative.
That is, the exclamation mark (!) means not. So, the if statement says: If the
variable does not match the pattern, execute the if block.
If you want to list a hyphen (-) as part of a set of allowable characters surrounded
by square brackets ([ ]), you must list the hyphen at the beginning
or at the end of the list. Otherwise, if you put it between two characters, the
script will interpret it as the range between the two characters, such as A-Z.
214 Part IV: Common PHP Applications
Using a script to create, display, and validate a form
The script in Listing 10-4 validates data received from a form. The script displays
the empty form when it is first run. When the user submits the form, the
same script is run again, and the form information is passed to it. The script
checks the form fields for blank fields and for incorrectly formatted fields. If it
finds errors, it displays an error message and redisplays the form. If all the
form information passes the checks, the script displays the user’s name and
address.
The script requires two include files. One file, shown in Listing 10-5, creates
an array that is used to build the form. The other include file, shown in Listing
10-6, displays the form.
Listing 10-4: A Script That Checks All the Data in the Form Fields
<?php
/* Script name: validateForm
* Description: Displays and validates a form that
* collects a name and address.
*/
include(“info.inc”); #6
#################################
## First display of empty form ##
#################################
if(!isset($_POST[‘Submit’])) #10
{
include(“addressForm.inc”);
}
########################################################
## Check information when form is submitted. Build ##
## arrays of blank and incorrectly formatted fields. ##
## If any errors are found, display error messages ##
## and redisplay form. If no errors found, display ##
## the submitted information. ##
########################################################
else #21
{
foreach($_POST as $field=>$value) #23
{
if(empty($_POST[$field])) #25
{
if($field != “midName”)
{
$blanks[$field] = “blank”; #29
}
}
(continued)
215 Chapter 10: The Basics of Web Applications
Listing 10-4 (continued)
else #33
{
$value = trim($value);
if($field != “zipcode”)
{
if(!ereg(“^[A-Za-z0-9’ .-]{1,65}$”,$value))
{
$formats[$field] = “bad”;
}
}
elseif($field == “zipcode”)
{
if(!ereg(“^[0-9]{5}(\-[0-9]{4})?”,$value))
{
$formats[$field] = “bad”;
}
}
}
} #51
### if any fields were not okay, display error ###
### message and redisplay form ###
if (@sizeof($blanks) > 0 or @sizeof($formats) > 0) #54
{
if (@sizeof($blanks) > 0)
{
echo “<b>You didn’t fill in one or more
required fields. You must enter:</b><br>”;
foreach($blanks as $field => $value)
{
echo “ {$labels[$field]}<br>”;
}
}
if (@sizeof($formats) > 0)
{
echo “<b>One or more fields have information that
appears to be incorrect. Correct the
format for:</b><br>”;
foreach($formats as $field => $value)
{
echo “ {$labels[$field]}<br>”;
}
}
echo “<hr>”;
include(“addressForm.inc”);
}
else #78
{
216 Part IV: Common PHP Applications
### If no errors in the form, display the ###
### name and address submitted by user ###
echo “<html><head><title>Name and Address
</title></head><body>\n”;
foreach($_POST as $field=>$value)
{
if($field != “Submit”)
{
echo “{$labels[$field]} $value<br>\n”;
}
}
echo “</body></html>”;
}
}
?>
I have added line numbers at the end of some of the lines in Listing 10-4 to
point out some important points in the script, as described in the following
list:
Line 6: This statement includes a file called info.inc that creates
an array called labels with information used later in the script. The
included file is shown in Listing 10-5. (See Chapter 8 for more on including
files in scripts.)
Line 10: This if statement checks for the existence of Submit in the
$_POST array. The submit button in the form is given the name Submit.
Therefore, if the form has been submitted, Submit will be in $_POST. The
condition is negative, so if Submit does not exist, the block is executed.
The block just includes a file called addressForm.inc that displays the
form. The include file is shown in Listing 10-6. This block is executed the
first time the script is called and displays a blank form.
Line 21: This line starts the else block in which Submit does exist in
$_POST. This section executes when the user submits a form and validates
the data.
Line 23: This line starts a loop through each element in $_POST. This
foreach block checks each field in the form.
Line 25: This if statement checks whether each field is empty. If the
field is not blank, the script goes to line 33, which begins a block that
checks the format of the field.
Line 29: This statement adds an element to the array $blanks for each
field that is blank. However, notice that this line does not execute if
the field name is midName. That is because Middle Name is not a required
field, so it can be blank.
217 Chapter 10: The Basics of Web Applications
Line 33: This is an else statement. If a field is not blank, this else statement
checks whether the format is acceptable. It checks all the fields,
except zip code, to look for unacceptable characters. Acceptable characters
are letters, numbers, an apostrophe, a space, a dot, and a hyphen.
The zip code field is checked separately for its exact format. If any fields
have unacceptable characters or the zip code doesn’t have the correct
format, an element for the field is added to the $formats array.
Line 51: This is the end of the section that checks the form fields. At this
point, the script has created two arrays, $blanks and $formats, that
contain entries for any errors that were found. If no errors were found,
the arrays were not created.
Line 54: This if statement checks to see if any errors were found by
checking to see if the arrays $blanks and $formats were created. If
either array is found, the error message is displayed, and the form is
redisplayed, retaining the information that the user typed so it can be
corrected.
Line 78: This else statement executes if no errors were found in the
form information. The else block displays all the information that the
user submitted in the form.
Notice that the script in Listing 10-4 is quite generic. That is, it processes information
from any form, with the exception of the section that checks the format
of the data in the fields. The section between lines 33 and 50 is customized
for the specific form being validated. However, the other sections remain the
same for most forms.
Listing 10-5 shows the file that is included, which creates the array used to
display the form and the error messages.
Listing 10-5: An Include File That Creates the Array
<?php
/* Script name: info.inc
* Description: creates an array of labels for use in a
* form.
*/
$labels = array( “firstName”=>”First Name:”,
“midName”=>”Middle Name:”,
“lastName”=>”Last Name:”,
“street”=>”Street Address:”,
“city”=>”City:”,
“state”=>”State:”,
“zipcode”=>”Zipcode:”);
?>
218 Part IV: Common PHP Applications
Listing 10-6 shows the script that displays the form. This is based on the
script shown in Listing 10-1 that displays the form shown in Figure 10-2.
Listing 10-6: An Include File That Displays the Form
<?php
/* Script name: addressForm.inc
* Description: Script displays a form.
*/
echo “<html>
<head><title>Customer Address</title></head>
<body>”;
echo “<p align=’center’>
<form action=’validateForm.php’ method=’POST’>
<table width=’95%’ border=’0’ cellspacing=’0’
cellpadding=’2’>\n”;
foreach($labels as $field=>$value)
{
if(isset($_POST[$field])) #13
{
$value = $_POST[$field];
}
else
{
$value = “”;
}
echo “<tr><td align=’right’>{$labels[$field]}</br></td>
<td><input type=’text’ name=’$field’ size=’65’
maxlength=’65’
value=’$value’> </td> </tr>”;
}
echo “ </table>
<div align=’center’>
<p><input type=’Submit’ name=’Submit’
value=’Submit Address’></p></div>
</form>”;
?>
</body></html>
Notice that an if-else block begins on line 13. The block sets the values
that are displayed in the form fields. The first time the form is displayed, the
$_POST array does not exist, because the form has not been submitted yet.
Therefore, the if statement on line 13 checks whether the $_POST element
for the field exists. If it does not exist, $value is set to blank. If the $_POST
entry does exist, $value is set to the information that the user typed in. The
variable $value is then used when the form is displayed.
219 Chapter 10: The Basics of Web Applications
Notice that the line that creates the submit button includes a name attribute,
in this case, name=’Submit’, as follows:
<p><input type=’Submit’ name=’Submit’
value=’Submit Address’></p></div>
This causes the submit value to be included in the $_POST array. You can
include two submit buttons in your form, with the same name but different
values, and perform different actions based on which submit button the user
clicked. That is, you can use an if statement such as if($_POST[‘Submit’]
== “Submit Address”).
The Web page in Figure 10-4 results when users accidentally type their first
names into the middle name field and also type nonsense for their zip codes.
Notice that two error messages appear, indicating that the First Name field is
blank and that the zip code field contains incorrect information.
Cleaning information
If you check the format of the data carefully, you can often prevent the bad
guys from typing malicious characters into your form fields. If you can limit the
format of the input you accept, such as checking for a format for a zip code
or a telephone number, or limit the input characters to letters and numbers,
you can protect yourself fairly well. However, sometimes you need to accept
anything the user enters. Your users might need to type in mathematical symbols
or HTML code. For example, you might be writing a script for a bulletin
board and want users to be able to enter anything into their messages.
When user input can’t be restricted much, bad guys are able to enter malicious
code into your form fields. For example, they could enter an actual script by
using script tags. Depending on what you do with the information from the
form, the malicious script can run on your system or be downloaded to run
on the system of a visitor to your Web site.
PHP provides two functions that can clean the data, rendering it harmless:
strip_tags: This function removes all tags from the text, although you
can tell it to allow specific tags.
htmlspecialchars: This function changes some special characters with
meaning to HTML into an HTML format that allows them to be displayed
without any special meaning. The changes are as follows:
• < becomes <
• > becomes >
• & becomes &
220 Part IV: Common PHP Applications
It’s safest to remove all tags from the user input. To remove all tags, use the
following type of statement:
$last_name = strip_tags($last_name);
PHP looks for an opening < and removes it and everything else, until it finds a
closing > or reaches the end of the string. You can tell PHP that specific tags
are okay by using a statement like the following:
$last_name = strip_tags($last_name,”<b><i>”);
This statement tells PHP to remove all tags from the string in $last_name
except <b> and <i>.
You may need to allow users to enter < or > characters. For example, if users
are entering text that will be displayed in a Web page and they need to display
< or >, such as in a mathematical formula or to display HTML code, you don’t
want to remove the tags. You can change the tags to HTML entities, which
HTML will display on a Web page as symbols and will not interpret as tags.
You can change the tags with the following type of statement:
$message = htmlspecialchars($message);
The following example shows the difference between the two functions.
Suppose $message contains the following text, typed into your form by a user:
Use the <?php ?> tags to enclose PHP statements.
Figure 10-4:
The result of
processing
a form
with both
missing and
incorrect
information.
221 Chapter 10: The Basics of Web Applications
You can use the following statements to strip the tags from $message and
then echo the updated value:
$message = strip_tags($message);
echo $message;
The output of the echo statement is as follows:
Use the tags to enclose PHP statements.
However, you can use the following statements instead:
$message = htmlspecialchars($message);
echo $message;
In this case, the output is different:
Use the <?php ?> tags to enclose PHP statements.
This output displays in the browser as follows:
Use the <?php ?> tags to enclose PHP statements.
This source is displayed correctly, but because the browser does not interpret
it as a tag, the browser doesn’t try to process the text as a PHP section. It just
displays the source.
Another function useful for cleaning input is the trim function. Users often
accidentally add spaces to the beginning or ending of a form field. These extra
spaces sometimes cause problems, such as when you compare the input to a
pattern. Use a statement like the following to remove these spaces:
$last_name = trim($last_name);
222 Part IV: Common PHP Applications
Chapter 11
Other Web Applications
In This Chapter
Passing information from page to page
Using cookies
Using hidden fields in HTML forms
Using PHP session functions
Adding JavaScript to PHP scripts
The simplest Web applications collect information from users in HTML forms
and then utilize the information by displaying it, storing it, or using it in
conditional statements. (Some simple applications are shown in Chapter 10.)
However, Web applications can be much more complex than this. For example,
a shopping cart must collect different types of information; display this information;
keep track of what users have ordered; calculate prices, taxes, and
shipping; charge credit cards; and perform other tasks. Such complex applications
consist of several scripts that share information. And applications
may also accept complete files from users rather than just information in a
form.
This chapter discusses the basics of these complex Web applications.
Overcoming Statelessness
HTML pages are stateless. That is, HTML pages are independent from one
another. When a user clicks a link, the Web server sends a new page to the
user’s browser, but the browser doesn’t know anything about the previous
page. As far as the browser knows, this could be the first Web page ever in
the history of the world. For static Web pages, where the user simply views a
document, statelessness works fine. However, many dynamic Web applications
need information to pass from page to page. For example, you may want to
save a user’s name and then display the name on another page.
The next few sections discuss methods of passing information from page
to page.
Navigating Web Sites
with Multiple Pages
Most Web sites consist of more than one Web page. A static multipage Web
site provides a navigation system, consisting of links (which sometimes look
like buttons) that users click to move around in the Web site and to find the
desired page. A dynamic Web page can use links to move from one page to
another, but uses additional methods as well. The following methods are
used in PHP scripts to move users from one page to another on a Web site:
Echoing links: Links send users to a new page when the user clicks
the link.
Using forms: Forms move users from one page to another when the user
clicks the submit button.
Relocating users: PHP provides the header function that takes the user
to a new page without needing an action from the user.
These methods are described in more detail in the following sections.
Echoing links
Using PHP, you can echo HTML links, which the user can then click to see various
pages in your Web site. This is no different than echoing any other HTML
code. Just send the HTML for the links, as in the following:
echo “<a href=’newpage.php’>New Page</a>”;
Using forms
You can also use an HTML form to display another page, as described in
Chapter 10. The form tag specifies a script that processes the form information.
When the submit button is clicked, the specified script receives the data
from the form and displays a new Web page.
The form does not have to collect information in order to display a new page.
You can use an empty form on a Web page to provide a button that a user can
click to move to another page. For example, you may want to provide a button
labeled Cancel or Next for the user to click, even when you don’t want to collect
any information from the user. To do so, just use the HTML form tags and
include only an input statement for a submit button. The button then appears
by itself on the Web page, and the script specified in the form tag displays
when the user clicks the submit button.
224 Part IV: Common PHP Applications
Relocating users
PHP also provides a method to move a user from one page to another in your
Web site without requiring the user to click a link or a button. You can send a
message to the Web server that tells it to send a new page by using the PHP
header statement. The format of the header function that sends the user to
a new page is as follows:
header(“Location: URL”);
225 Chapter 11: Other Web Applications
Statements that must come before output
Some PHP statements can only be used before
sending any output to the browser. Header
statements, setcookie statements, and
session functions, all described in this chapter,
must all come before any output is sent. If
you use one of these statements after sending
output, you may see the following message:
Warning: Cannot modify header
information – headers
already sent by (output
started at /test.php:2) in
/test.php on line 3
The message provides the name of the file and
indicates which line sent the previous output. Or
you may not see a message at all; the new page
may just not appear. (Whether you see an error
message depends on what error message level
is set in PHP; see Chapter 4 for details.) The following
statements fail because the header message
is not the first output (an HTML section
comes before the header statement):
<html>
<head><title>testing
header</title></head>
<body>
<?php
header(“Location:
http://janetscompany.com”);
?>
</body></html>
As you can see, three lines of HTML code
are sent before the header statement. The
following statements work, although they don’t
make much sense, because the HTML lines are
after the header statement — that is, after the
user has already been taken to another page:
<?php
header(“Location:
http://janetscompany.com”);
?>
<html>
<head><title>testing
header</title></head>
<body>
</body>
</html>
The following statements fail:
<?php
header(“Location:
http://company.com”);
?>
<html>
<head><title>testing
header</title></head>
<body>
</body></html>
The reason these statements fail is not easy to
see, but if you look closely, you will notice a
single blank space before the opening PHP tag.
This blank space is output to the browser,
although the resulting Web page looks empty.
Therefore, the header statement fails because
there is output before it. This is a common mistake
and difficult to spot.
The header statement sends the message, Location: URL, to the Web server.
In response, the file located at URL is sent to the user’s browser. Either of the
following statements are valid header statements:
header(“Location: newpage.php”);
header(“Location: http://company.com/catalog/catalog.php”);
The header function has a major limitation. The header statement can only
be used before any other output is sent. You can’t echo output — such as
some HTML code — to the Web page and then send a message requesting a
new page in the middle of the script. The header statement is not the only
PHP statement that has this restriction. See the nearby sidebar for a discussion
of the header statement and other statements like it that must come
before output.
In spite of its limitations, the header statement is useful. It’s the only way to
move users to a new page without requiring an action from the user. Therefore,
it’s really the only statement that can be used in conditional statements to
display alternate pages to different users. The following example shows how
to display alternate pages based on the type of user account:
<?php
if ($typeAcct == “admin”)
{
header(“Location: AdminPage.php”);
}
else
{
header(“Location: SiteHomePage.php”);
}
?>
These statements run a script that displays an admin page for users with an
admin account, but displays a general page for other users. You can have as
many PHP statements as you want before the header function, as long as
they don’t send output. You can’t have any HTML sections before the header,
because HTML is always sent to the browser.
Moving Information from Page to Page
No matter how the user gets from one page to the next, you may need information
from the first page to be available on the next page. With PHP, you can
move information from page to page by using any of the following methods:
226 Part IV: Common PHP Applications
Adding information to the URL: You can add specific information to the
end of the URL of the new page. This method is most appropriate when
you need to pass only a small amount of information.
Storing information via cookies: You can store cookies — small amounts
of information containing variable=value pairs — on the user’s computer.
After the cookie is stored, you can retrieve it from any Web page.
However, users can refuse to accept cookies, so this method doesn’t
work in all environments.
Passing information using HTML forms: You can pass information that
is in a form. When the user clicks the submit button, the information in
the form is sent to the next script. This method is useful when you need
to collect information from users.
Using PHP session functions: Beginning with PHP 4, PHP functions are
available that set up a user session and store session information on the
server; this information can be accessed from any Web page. This method
is useful for sessions in which you expect users to view many pages.
The next few sections discuss these options in greater detail.
Adding information to the URL
A simple way to move any information from one page to the next is to add the
information to the URL you’re linking to. To do so, you put the information in
the following format:
variable=value
In this case, the variable is a variable name, but you do not use a dollar sign
($) in it. The value is the value to be stored in the variable. You can add the
variable=value pairs anywhere you use a URL. You signal the start of the
information with a question mark (?). The following statements are all valid
ways of passing information in the URL:
<a href=”nextpage.php?age=14”>go to next page</a>
header(“Location: nextpage.php?age=14”);
<form action=”nextpage.php?age=14” method=”POST”>
These examples all send the variable $age with the value 14 assigned to it.
The variable/value pair is sent to nextpage.php by adding the pair to the
end of the URL.
227 Chapter 11: Other Web Applications
You can add several variable=value pairs, separating each pair with an
ampersand (&) as follows:
<form action=”nextpage.php?state=CA&city=Mall” method=”POST”>
Any information passed into a URL is available in the built-in array $_GET. In
the preceding example, the script nextpage.php could use the following
statements to display the information passed to it:
echo “{$_GET[‘city’]}, {$_GET[‘state’]};
The output is as follows:
Mall, CA
The information is also available in the built-in array $_REQUEST. You can use
the following statements to get the same result:
echo “{$_REQUEST[‘city’]}, {$_REQUEST[‘state’]};
Passing information in the URL is easy, especially for small amounts of information.
However, this method has some disadvantages, including some
important security issues. Here are some reasons you may not want to pass
information in the URL:
The whole world can see it. The URL is shown in the address line of the
browser, which means that the information you attach to the URL is also
shown. If the information needs to be secure, you don’t want it shown so
publicly. For example, if you’re moving a password from one page to the
next, you probably don’t want to pass it in the URL.
A user can send information in the URL, just as easily as you can. For
example, suppose that after a user logs into your restricted Web site, you
add auth=yes to the URL. On each Web page, you check to see if $_GET
[‘auth’] = yes. If so, you let the user see the Web page. However, any
user can type http://www.yoursite.com/page.php?auth=yes into
his browser and be allowed to enter without logging in.
The user can bookmark the URL. You may not want your users to save
the information you add to the URL.
The length of the URL is limited. The limit differs for various browsers
and browser versions, but a limit always exists. Therefore, if you’re passing
a lot of information, the URL may not have room for it.
228 Part IV: Common PHP Applications
Passing information via cookies
You can store information as cookies, which are small amounts of information
containing variable=value pairs, similar to the pairs you can add to a URL.
The user’s browser stores cookies on the user’s computer. Your scripts can
then use the cookie information.
At first glance, cookies seem to solve the problem of moving data from page
to page. Just stash a cookie on the user’s computer and get it whenever you
need it. In fact, the cookie can be stored so that it remains there after the user
leaves your site and will still be available when the user enters your Web site
a month later. Problem solved? Well, not exactly. Cookies are not under your
control. They are under the user’s control. The user can at any time delete the
cookie. In fact, users can set their browsers to refuse to allow any cookies,
and many users do refuse cookies or routinely delete them. Many users are
not comfortable with the idea of a stranger storing things on their computers,
especially files that remain after they leave the stranger’s Web site. This is an
understandable attitude. However, it definitely limits the usefulness of cookies.
If your application depends on cookies and the user has cookies shut off,
your application won’t work for that user.
Cookies were originally designed for storing small amounts of information for
short periods of time. Unless you specifically set the cookie to last a longer
period of time, the cookie will disappear when the user leaves your Web site.
Although cookies are useful in some situations, consider the following points
before deciding to use them:
Users may set their browsers to refuse cookies. Unless you know for
sure that all your users will have cookies turned on or you can request
that they turn on cookies and expect them to follow your request, cookies
are a problem. If your application depends on cookies, it won’t run if
cookies are turned off.
PHP has features that work better than cookies. Beginning with
PHP 4, PHP sessions can store information that is available for the
entire session — in other words, as long as the user stays at your Web
site. Session functions store information on the server, where it is not
at the mercy of the user. Sessions, however, don’t work for long-term
storage of information.
You can store data in a database. If you have access to a database where
you can store and retrieve data, this is often a better solution than cookies.
Users can’t delete the data in your database unexpectedly.
229 Chapter 11: Other Web Applications
Storing and retrieving information in cookies
You store cookies by using the setcookie function. The general format is as
follows:
setcookie(“variable”,”value”);
The variable is the variable name, but you do not include the dollar sign
($).This statement stores the information only until the user leaves your Web
site. For example, the following statement stores the pair state=CA in the
cookie file on the user’s computer:
setcookie(“state”,”CA”);
When the user moves to the next page, the cookie information is available in
the built-in array called $_COOKIE. The next Web page can display the information
from the cookie by using the following statement.
echo “Your home state is “.$_COOKIE[‘state’];
The output from this statement is as follows:
Your home state is CA
The cookie is not available in the script where it is set. The user must go to
another page or redisplay the current page before the cookie information is
available.
Setting expiration dates
If you want the information stored in a cookie to remain in a file on the user’s
computer after the user leaves your Web site, set your cookie with an expiration
time, as follows:
setcookie(“variable”,”value”,expiretime);
The expiretime value sets the time when the cookie expires. The value for
expiretime is usually set by using either the time or mktime function as
follows:
time: This function returns the current time in a format the computer can
understand. You use the time function plus a number of seconds to set
the expiration time of the cookie, as shown in the following statements:
setcookie(“state”,”CA”,time()+3600); #expires in one hour
setcookie(“Name”,$Name,time()+(3*86400)) #expires 3 days
230 Part IV: Common PHP Applications
mktime: This function returns a date and time in a format that the computer
can understand. You must provide the desired date and time in
the following order: hour, minute, second, month, day, and year. If any
value is not included, the current value is used. You use the mktime
function to set the expiration time of the cookie, as shown in the following
statements:
setcookie(“state”,”CA”,mktime(3,0,0,4,1,2003)); #expires
at 3:00 AM on April 1, 2003
setcookie(“state”,”CA”,mktime(13,0,0,,,)); /#expires at
1:00 PM
today
You can remove a cookie by setting its value to nothing. Either of the following
statements removes the cookie:
setcookie(“name”);
setcookie(“name”,””);
The setcookie function has a major limitation, however. The setcookie
function can only be used before any other output is sent. You cannot set a
cookie in the middle of a script, after you have echoed some output to the
Web page. For more information, see the see the sidebar in this chapter
called “Statements that must come before output.”
Passing information using HTML forms
The most common way to pass information from one page to another is by
using HTML forms. An HTML form is displayed with a submit button. When
the user clicks the submit button, the information in the form fields is passed
to the script included in the form tag. The general format is as follows:
<form action=”processform.php” method=”POST”>
tags for one or more fields
<input type=”submit” value=”string”>
</form>
The most common use of a form is to collect information from users and pass
it to the next page (discussed in detail in Chapter 10). However, forms can also
be used to pass other types of information.
Hidden fields are fields in forms that send information to the next page without
appearing in the form on the Web page. Hidden fields can be included in
the form along with other types of fields, or can be the only type of field in the
form. When the user clicks the submit button, the information in the hidden
231 Chapter 11: Other Web Applications
field is sent to the next page. For example, the following statements pass the
user’s account type to the next page when the user clicks a button that says
Next Page:
<?php
$acct = “admin”;
echo “<form action=’nextpage.php’ method=’POST’>
<input type=’hidden’ name=’acct’ value=’$acct’>
<input type=’submit’ value=’Next Page’>
</form>\n”;
?>
The Web page shows a submit button that says Next Page, but it doesn’t ask
the user for any information. When the user clicks the button, nextpage.php
runs, and the account type is available in $_POST[‘acct’]. In this way, you
can pass information that you need to use other places in the Web site from
page to page. In this example, you could use this code as part of a script that
displays some products. When the user clicks the Next Page button, the
account type is sent to the new page for use in that script.
Using PHP sessions
A session is the time that a user spends at your Web site. Users may view many
Web pages between the time they enter your site and leave it. Often you want
information to be available for a complete session. Beginning with version 4.0,
PHP provides a way to do this.
Understanding how PHP sessions work
PHP allows you to set up a session and store session variables. After you
create a session, the session variables are available for your use on any other
Web page. To make session information available, PHP does the following:
1. PHP assigns a session ID number.
The number is a really long nonsense number that is unique for the user
and that no one could possibly guess. The session ID is stored in a PHP
system variable named PHPSESSID.
2. PHP stores the variables that you want saved for the session in a file on
the server.
The file is named with the session ID number. It’s stored in a directory
specified by session.save_path in the php.ini file. The session directory
must exist before session files can be saved in it.
3. PHP passes the session ID number to every page.
232 Part IV: Common PHP Applications
If the user has cookies turned on, PHP passes the session ID by using
cookies. If the user has cookies turned off, PHP behavior depends on
whether trans-sid is turned on in php.ini. (You find out more about
trans-id in the section “Using sessions without cookies,” later in this
chapter.)
4. PHP gets the variables from the session file for each new session page.
Whenever a user opens a new page that is part of the session, PHP
gets the variables from the file by using the session ID number that
was passed from the previous page. The variables are available in the
$_SESSION array.
For PHP 4.1.2 or earlier, trans-sid is not available unless it was enabled by
using the option –enable-trans-sid when PHP was compiled.
Opening and closing sessions
You should open a session at the beginning of each Web page. Open the session
with the session_start function, as follows:
session_start();
The function first checks for an existing session ID number. If it finds one, it
sets up the session variables. If it doesn’t find one, it starts a new session by
creating a new session ID number.
Because sessions use cookies, if the user has them turned on, session_start
is subject to the same limitation as cookies. That is, to avoid an error, the
session_start function must be called before any output is sent. For complete
details, see the sidebar in this chapter called “Statements that must
come before output.”
You can tell PHP that every page on your site should automatically start with a
session_start statement. You can do this with a setting in the configuration
file php.ini. If you’re the PHP administrator, you can edit this file; otherwise,
ask the administrator to edit it. Look for the variable session.auto_start
and set its value to 1. You may have to restart the Web server before this
setting takes effect. With auto_start turned on, you do not need to add a
session_start at the beginning of each page.
You may want to restrict your site to users with a valid user ID and password.
For restricted sessions that users log into, you often want users to log out
when they’re finished. To close a session, use the following statement wherever
to want to close the session:
session_destroy();
233 Chapter 11: Other Web Applications
This statement gets rid of all the session variable information that is stored in
the session file. PHP no longer passes the session ID number to the next page.
However, the statement does not affect the variables set on the current page;
they still hold the same values. If you want to remove the variables from the
current page, as well as prevent them from being passed to the next page,
unset them by using this statement:
unset($variablename1,$variablename2,…);
Using PHP session variables
To save a variable in a session so that it’s available on later Web pages, store
the value in the $_SESSION array, as follows:
$_SESSION[‘varname’] = “John Smith”;
When you open a session on any subsequent Web page, the values stored in
the $_SESSION array are available.
If you want to stop storing any variable at any time, you can unset the variable
by using the following statement:
unset($_SESSION[‘varname’];
The following two scripts show how to use sessions to pass information from
one page to the next. The script in Listing 11-1 shows the first page of a session.
Listing 11-2 shows the second page in a session.
Listing 11-1: Starting a Session
<?php
/* Script name: sessionTest1.php
* Description: Starts a session. Saves a session variable.
*/
session_start();
$_SESSION[‘session_var’] = “testing”;
?>
<html>
<head><title>Testing Sessions page 1</title></head>
<body>
<p>This is a test of the sessions feature.
<form action=”sessionTest2.php” method=”POST”>
<input type=”text” name=”form_var” value=”testing”>
<input type=”submit” value=”Go to Next Page”>
</form>
</body>
</html>
234 Part IV: Common PHP Applications
In this script, a session is started and one session variable is stored called
session_var. A form is also displayed with one text field where the user can
enter some text. When the submit button from this form, labeled “Go to Next
Page” is clicked, the sessionTest2.php script runs.
Listing 11-2: The Second Page of a Session
<?php
/* Script name: sessionTest2.php
* Description: Gets a variable from an existing session.
*/
session_start();
?>
<html>
<head><title>Testing Sessions page 2</title></head>
<body>
<?php
$session_var = $_SESSION[‘session_var’];
$form_var = $_POST[‘form_var’];
echo “session_var = $session_var<br>\n”;
echo “form_var = $form_var<br>\n”;
?>
</body>
</html>
This script displays the variables that were passed from the previous script
(sessionTest1.php).
If users pointed their browsers at sessionTest1.php and clicked the submit
button that says Go to Next Page, they’d see the following output from
sessionTest2.php:
session_var = testing
form_var = testing
As you can see, both the session variable, session_var and the form variable,
form_var are available in the built-in arrays to be echoed from this script.
Using sessions without cookies
Many users turn off cookies in their browsers. PHP checks the user’s browser
to see whether cookies are allowed and behaves accordingly. If the user’s
browser allows cookies, PHP does the following:
It sets the variable $PHPSESSID equal to the session ID number.
It uses cookies to move $PHPSESSID from one page to the next.
235 Chapter 11: Other Web Applications
If the user’s browser is set to refuse cookies, PHP behaves differently:
It sets a constant called SID. The constant contains a variable=value
pair that looks like PHPSESSID=longstringofnumbers. (The long string
of numbers is the session ID.)
It may or may not move the session ID number from one page to the
next, depending on whether trans-sid is turned on. If trans-sid is
turned on, PHP passes the session ID number; if it is not turned on, PHP
does not pass the session ID number.
trans-sid is turned off by default. You can turn it on by editing your php.
ini file. Search for the line that begins with session.use_trans_id = . If
the setting is 0, trans_id is off; if the setting is 1, trans_id is on. To turn the
setting on when it is off, change 0 to 1. You may have to restart your Web
server before the new setting takes effect.
Turning trans-sid on has advantages and disadvantages:
Advantages: Sessions work seamlessly even when users turn cookies
off. You can script sessions easier, without being concerned about the
user’s browser setting for cookies.
Disadvantages: The session ID number is often passed in the URL. In
some situations, for security reasons, the session ID number should not
be shown in the browser address. Also, when the session ID number is
in the URL, it can be bookmarked by the user. Then, if the user returns to
your site by using the bookmark with the session ID number in it, the new
session ID number from the current visit can get confused with the old
session ID number from the previous visit and possibly cause problems.
Sessions with trans-sid turned on
When trans-sid is turned on and the user has cookies turned off, PHP automatically
sends the session ID number in the URL or as a hidden form field.
If the user moves to the next page by using a link, a header function, or a
form with the GET method, the session ID number is added to the URL. If the
user moves to the next page by using a form with the POST method, the session
ID number is passed in a hidden field. PHP recognizes PHPSESSID as the
session ID number and handles the session without any special programming
on your part.
The session ID number is added only to the URLs for pages on your Web site.
If the URL of the next page includes a server name, PHP assumes that the URL
is on another Web site and does not add the session ID number. For example,
suppose your link statement is as follows:
<a href=”newpage.php”>
PHP will add the session ID number. However, suppose your statement is as
follows:
236 Part IV: Common PHP Applications
<a href=”HTTP://www.janetscompany.com/newpage.php”>
PHP will not add the session ID number.
Sessions without trans-sid turned on
When trans-sid is not turned on and the user has cookies turned off, PHP
does not send the session ID number to the next page. Instead, you must send
the session ID number yourself.
Fortunately, PHP provides a constant that you can use to send the session ID
yourself. This constant is named SID and contains a variable=value pair
that you can add to the URL, as follows:
<a href=”nextpage.php?<?php echo SID?> > next page </a>
This link statement includes the question mark (?) at the end of the filename
and the constant SID added to the URL. SID contains the session ID number.
The output from echo SID looks something like this:
PHPSESSID=877c22163d8df9deb342c7333cfe38a7
Therefore, the URL of the next page looks as follows:
nextpage.php?PHPSESSID=877c22163d8df9deb342c7333cfe38a7
The session ID is added to the end of the URL. For one of several reasons
(discussed earlier in this chapter), you may not want the session ID number
to appear on the URL shown by the browser. To prevent this, you can send
the session ID number in a hidden field in a form by using the POST method.
First, get the session ID number, and then send it in a hidden field. The following
statements do this:
<?php
$PHPSESSID = session_id();
echo “<form action=’nextpage.php’ method=’POST’>
<input type=’hidden’ name=’PHPSESSID’
value=’$PHPSESSID’>
<input type=’submit’ value=’Next Page’>
</form>”;
?>
These statements do the following:
1. The function session_id, which returns the current session ID number,
stores the session ID number in the variable $PHPSESSID.
2. $PHPSESSID is sent in a hidden form field.
On the new page, PHP automatically finds PHPSESSID without any special
programming needed from you.
237 Chapter 11: Other Web Applications
Creating sessions for members only
PHP session functions are ideal for Web sites that are restricted and require
users to login with a login name and password. These types of Web sites
undoubtedly have many pages, and you don’t want the user to have to login
to each page. PHP sessions can keep track of whether the user has logged in
and refuse access to users who aren’t logged in. Using PHP sessions, you can
do the following:
1. Show users a login page.
2. If a user logs in successfully, set and store a session variable.
3. Whenever a user goes to a new page, check the session variable to see if
the user has logged in.
4. If the user has logged in, show the page.
5. If the user has not logged in, bring up the login page.
To check whether a user has logged in, add the following statements to the
top of every page:
<?php
session_start()
if ( @$_SESSION[‘login’] != “go” )
{
header(“Location: loginPage.php”);
exit();
}
?>
In these statements, PHP checks a session variable called login — which was
set at login — to see whether $_SESSION[‘login’] is equal to “go”. If it is
not, it means the user is not logged in, and the user is sent to the login page.
If $_SESSION[‘login’] equals “go”, the script proceeds with the rest of the
statements on the Web page.
Uploading Files
You may want users to upload files to your Web site. For example, you may
want users to be able to upload resumes to your job-search Web site or pictures
to your photo album Web site.
238 Part IV: Common PHP Applications
Using a form to upload a file
You can display a form that allows a user to upload a file by using an HTML
form designed for that purpose. The general format of the form is as follows:
<form enctype=”multipart/form-data”
action=”processfile.php” method=”POST”>
<input type=”hidden” name=”MAX_FILE_SIZE” value=”30000”>
<input type=”file” name=”user_file”>
<input type=”submit” value=”Upload File”>
</form>
Notice the following points regarding the form:
The enctype attribute is used in the form tag. You must set this attribute
to multipart/form-data when uploading a file to ensure the file arrives
correctly.
A hidden field is included that sends a value (in bytes) for MAX_FILE_
SIZE. If the user tries to upload a file that is larger than this value, it
won’t upload. When sending the value for MAX_FILE_SIZE in your form,
you need to consider two size settings in php.ini, as follows
• upload_max_filesize: The MAX_FILE_SIZE you send in your
upload form can’t be larger than the value of upload_max_
filesize. If you are uploading a larger file and need to send a MAX_
FILE_SIZE larger than the current value of upload_max_filesize,
you need to increase the value of upload_max_filesize by editing
the php.ini file. The default value for this setting is 2M.
• post_max_size: The total amount of information you send in a
POST form can’t be larger than the value of post_max_size. The
default value for this setting is 8M. You can increase this value if
necessary by editing your php.ini file.
The input field that uploads the file is of type file.
The value for MAX_FILE_SIZE must be sent before the file is uploaded if you
want the file size limit to apply to the uploading file.
When the user submits the form, the file is uploaded to a temporary location.
The script that processes the form needs to copy the file to another location
because the temporary file is deleted as soon as the script is finished. You
can use phpinfo() to see where the temporary files are stored. If you don’t
like the location of the temporary directory, you can change it by changing
upload_tmp_dir in the php.ini file. If no directory is specified in php.ini,
a default temporary directory is used. Because the temporary files are deleted
almost immediately, the location of the temporary directory is not likely to
be very important.
239 Chapter 11: Other Web Applications
Accessing information about
an uploaded file
Along with the file, information about the file is sent with the form. This information
is stored in the PHP built-in array called $_FILES. An array of information
is available for each file that was uploaded. As with any other form, you
can obtain the information from the array by using the name of the field. For
example, you can get information about the uploaded file from the following
array:
$_FILES[‘fieldname’][‘name’]
$_FILES[‘fieldname’][‘type’]
$_FILES[‘fieldname’][‘tmp_name’]
$_FILES[‘fieldname’][‘size’]
For example, suppose you use the following field to upload a file:
<input type=”file” name=”user_file”>
If the user uploads a file named test.txt by using the form, the resulting
array that can be used by the processing script looks something like this:
$_FILES[user_file][name] = test.txt
$_FILES[user_file][type] = text/plain
$_FILES[user_file][tmp_name] = D:\WINNT\php92C.tmp
$_FILES[user_file][size] = 435
In this array, name is the name of the file that was uploaded, type is the type
of file, tmp_name is the path/filename of the temporary file, and size is the
size of the file. Notice that name contains only the filename, while tmp_name
includes the path to the file as well as the filename.
If the file is too large to upload, the tmp_name in the array is set to none, and
the size is set to 0.
By default, PHP stores the temporary uploaded file in your system directory
on Windows (Windows for Win98/XP and Winnt for Win2000) or /tmp on Unix/
Linux. You can change the location where the temporary files are stored by
setting the location in php.ini. Look in your php.ini file for the following
line:
;upload_tmp_dir =
240 Part IV: Common PHP Applications
Remove the semicolon at the beginning of the line so that the line becomes
active. Add the path to the directory where you want the temporary files to
be stored. Your active line looks similar to the following:
upload_tmp_dir = d:\tempfiles
The directory tempfiles must exist. If it doesn’t, PHP ignores the setting and
continues to save the files in the default location.
Moving uploaded files to their destination
The general format of the statement that moves the file is as follows:
move_uploaded_file(path/tempfilename,path/permfilename);
The tmp_file element in $_FILES stores the temporary filename and location,
so you can use the following statement to move the file to your desired
location, in this case, c:\data\new_file.txt:
move_uploaded_file($_FILES[‘user_file’][‘tmp_name’],
‘c:\data\new_file.txt’);
The destination directory (in this case, c:\data) must exist before the file
can be moved to it. This statement doesn’t create the destination directory.
Security can be an issue when uploading files. Allowing strangers to load files
onto your computer is risky; malicious files are possible. So, you probably
want to check the files for as many factors as possible after they are uploaded,
using conditional statements to check file characteristics, such as checking
for the expected file type and for the size. In some cases, for even more security,
it may be a good idea to change the name of the file to something else so
users don’t know where their files are or what they’re called.
Putting it all together
A complete example script is shown in Listing 11-3. This script displays a
form for the user to upload an image file, saves the uploaded file, and then
displays a message after the file has been successfully uploaded. This script
expects the uploaded file to be an image file, and tests to make sure that it is
an image file, but any type of file can be uploaded. The form displayed by this
script is shown in Figure 11-1.
241 Chapter 11: Other Web Applications
Listing 11-3: A Script That Uploads a File Using a POST Form
<?php
/* Script name: uploadFile.php
* Description: Uploads a file via HTTP using a POST form.
*/
if(!isset($_POST[‘Upload’])) #5
{
include(“form_upload.inc”);
} # endif
else #9
{
if($_FILES[‘pix’][‘tmp_name’] == “none”) #11
{
echo “<b>File did not successfully upload. Check the
file size. File must be less than 500K.<br>”;
include(“form_upload.inc”);
exit();
}
if(!ereg(“image”,$_FILES[‘pix’][‘type’])) #16
{
echo “<b>File is not a picture. Please try another
file.</b><br>”;
include(“form_upload.inc”);
exit();
}
else #23
{
$destination = ‘c:\data’.”\\”.$_FILES[‘pix’][‘name’];
$temp_file = $_FILES[‘pix’][‘tmp_name’];
move_uploaded_file($temp_file,$destination);
echo “<p><b>The file has successfully uploaded:</b>
{$_FILES[‘pix’][‘name’]}
({$_FILES[‘pix’][‘size’]})</p>”;
}
}
?>
I have added line numbers at the end of some of the lines in the script. The
script is discussed below with reference to these line numbers:
Line 5: This line is an if statement that tests whether the form has been
submitted. If not, the form is displayed by including the file containing
the form code. The include file is shown in Listing 11-4.
Line 9: This line starts an else block that executes if the form has been
submitted. This block includes the rest of the script and processes the
submitted form and uploaded file.
Line 11: This line is an if statement that tests whether the file was successfully
uploaded. If not, an error message is displayed, and the form is
redisplayed.
242 Part IV: Common PHP Applications
Line 16: This line is an if statement that tests whether the file is a picture.
If not, an error message is displayed, and the form is redisplayed.
Line 23: This line starts an else block that executes if the file has been
successfully uploaded. The file is moved to its permanent destination,
and a message is displayed that the file has been uploaded.
Listing 11-4 shows the include file used to display the upload form.
Listing 11-4: An Include File That Displays the File Upload Form
<!– Script Name: form_upload.inc
Description: Displays a form to upload a file –>
<html>
<head><title>File Upload</title></head>
<body>
<ol><li>Enter the name of the picture you want to upload
to our picture archive or use the browse button
to navigate to the picture file.</li>
<li>When the path to the picture file shows in the text
field, click the Upload Picture button.</li>
</ol>
<div align=”center”><hr>
<form enctype=”multipart/form-data”
action=”uploadFile.php” method=”POST”>
<input type=”hidden” name=”MAX_FILE_SIZE” value=”500000”>
<input type=”file” name=”pix” size=”60”>
<p><input type=”submit” name=”Upload”
value=”Upload Picture”>
</form>
</body></html>
Figure 11-1:
A form that
allows users
to upload an
image file.
243 Chapter 11: Other Web Applications
Notice that the include file doesn’t contain PHP code, just HTML code.
The form that allows users to select a file to upload is shown in Figure 11-1.
The form has a text field for inputting a filename and a browse button that
enables the user to navigate to the file and select it.
Using JavaScript with PHP
You may want to use JavaScript in your Web page. For example, you may want
your Web page to change based on the position of the mouse pointer or a click
of the mouse. Or you may want to modify some information on your Web page
without redisplaying the entire page. You can’t achieve these effects with PHP
because it’s strictly a server-side scripting language. PHP doesn’t know what
is happening on the user’s PC; it only knows what’s happening on the Web site
server. If you want to make changes to the Web page display without resending
the Web page from the server, you need to use a client-side scripting language,
like JavaScript.
The user can turn off JavaScript so that the browser doesn’t execute the
JavaScript statements. It’s not wise for your Web application to depend
on JavaScript unless you can ensure that all your users have JavaScript
enabled in their browsers.
I don’t talk about the JavaScript language in this chapter. I assume that you
either know JavaScript or can learn the actual JavaScript code elsewhere. In
this chapter, I talk about how to use JavaScript in a PHP script. (For more
information on JavaScript, check out JavaScript For Dummies, 3rd Edition, by
Emily A. Vander Veer.)
Adding JavaScript code to a PHP script
JavaScript code, just like HTML code, is understood and executed by the
browser on the user’s computer (the client side). Therefore, you add
JavaScript to a PHP script in the same way that you add HTML to a PHP
script. In fact, JavaScript is basically part of the HTML code for the Web
page. You add JavaScript to the HTML by using an HTML tag, as follows:
<script language=”JavaScript”>
JavaScript code
</script>
244 Part IV: Common PHP Applications
JavaScript code is used in your PHP script in the same way HTML code is
used — namely, it is echoed. For example, the following statements send
some JavaScript to the browser:
<?php
echo “<script language=\”JavaScript\”>
<!–
document.write(‘This page last updated: ‘
+ document.lastModified + ‘<br>’)
// –>
</script>”;
?>
When a browser receives these JavaScript statements, it executes them and
produces the following output:
This page last updated: 03/24/2003 12:01:47
This is the date and time that the file containing the script was last modified.
You can use JavaScript statements alone, outside of PHP tags, just as you can
HTML code. You could add the preceding statements to a PHP file without
using PHP tags or an echo statement. If the JavaScript statement is not added
in a PHP section, it is sent to the browser exactly as is, without being passed
to the PHP script, just as HTML code is when it’s outside of a PHP section.
Using PHP variables with JavaScript
You can use PHP variables with JavaScript the same way you do with HTML.
You can add the variable to the JavaScript code. For example, the JavaScript
example in the preceding section can include a PHP variable, as follows:
<?php
$string = “This page last updated: “;
echo “<script language=\”JavaScript\”>
<!–
document.write(‘$string’
+ document.lastModified + ‘<br>’)
// –>
</script>”;
?>
245 Chapter 11: Other Web Applications
The JavaScript language itself uses variables. You can set a JavaScript variable
to the value of a PHP variable to use in your JavaScript code. For example, the
JavaScript could be sent as follows:
<?php
$string = “This page last updated: “;
echo “<script language=\”JavaScript\”>
<!–
var message = \”$string\”;
document.write( message
+ document.lastModified + ‘<br>’)
// –>
</script>”;
?>
Because JavaScript code is not executed until it reaches the browser on the
client side, passing values from JavaScript variables to PHP variables can’t
take place in the current page. The JavaScript value must be passed on to the
next PHP script before PHP can receive it. JavaScript can pass the values on
so that PHP can use them by adding them to the URL, by storing them in a
cookie that PHP can read, or by sending them as a form element.
246 Part IV: Common PHP Applications
Chapter 12
Storing Data with PHP
In This Chapter
Writing and reading flat files
Exchanging data between PHP and other programs
Understanding database support in PHP
Using PHP to interact with a database
Handling database-connection errors
Many applications require the long-term storage of information. In PHP
scripts, you can make information available within sessions — periods
of time that users spend at your Web site — by using methods such as PHP
session functions and by submitting forms. However, eventually you need to
store information for use tomorrow or next week. You can store it in a cookie
that you set to last after the session is ended (as discussed in Chapter 11), but
the information is vulnerable. It’s not under your control. The user can delete
or change the information at any time or can refuse to accept the cookie. To be
available and stable, the information needs to be stored somewhere secure,
where no one can access or tamper with it. The information needs to be stored
on the server.
Information can be stored on the server in flat files or in databases. Flat files
are text files stored in the computer file system. Humans can read flat files by
using the operating system commands that display files, such as cat in Linux
and Unix. You can access and edit these files by using any text file editor, such
as Notepad or vi. The information in the flat file is stored as strings, and the
PHP script that retrieves the data needs to know how the data is stored. For
example, to retrieve a customer name from a file, the PHP script needs to
know that the customer name is stored in the first 20 characters of every line.
Using a database for data storage requires you to install and learn to use database
software, such as MySQL or Oracle. The data is stored in files created by
the database software and can only be accessed by the database software.
Databases can store very complex information that you can retrieve easily.
You don’t need to know how the data is stored, just how to interact with the
database software. For example, to retrieve a customer name, the PHP script
needs to know only how to tell the database software that it wants the customer
name, using a standard communication language called SQL, The database
software handles the storage and delivers the data, without the script
needing to know exactly where or how the customer name is stored.
Flat files have some advantages over databases:
Available and versatile: You can create and save data in any operating
system’s file system. You don’t need to install any extra software.
Additionally, text data stored in flat files can be read by a variety of
software programs, such as word processors or spreadsheets.
Easy to use: You don’t need to do any extra preparation, such as install
database software, design a database, create a database, and so on. Just
create the file and store the data with statements in your PHP script.
Smaller: Flat files store data by using less disk space than databases.
In summary, a flat file is quick and easy and takes less space than a database.
It is ideal for storing small amounts of information quickly, such as a simple
list or small piece of information. Flat files are particularly useful for making
information available to other software, such as an editing program or a
spreadsheet. Flat files can be looked at by anyone with access to the computer
directory where they are stored, so they are useful when information
needs to be made available to other people.
Databases have some advantages as well:
Security: A database provides a security layer of its own, in addition to
the security provided by the operating system. A database protects the
data from outside intrusion better than a flat file.
Accessibility of data: You can store data in a database by using a very
complex data structure, specifying data types and relationships among
the data. The organization of the data makes it easy to search the data
and retrieve what you need.
Ability to handle multiple users: When many users store or access data
in a single file, such as a file containing names and addresses, a database
ensures that users take their turn with the file to avoid overwriting each
other’s data.
In summary, databases require more start-up effort and use more space than
a flat file, but are much more suitable for handling complex information. The
database handles the internal organization of the data, making data retrieval
248 Part IV: Common PHP Applications
much simpler. A database provides more security, making it more suitable for
sensitive, private information. Databases can more easily and efficiently handle
high traffic when many users may try to access the data almost simultaneously.
In PHP 5, SQLite, an extension for data storage that combines the main advantages
of flat files and databases, is included by default. SQLite stores the data
in a flat file, so you don’t need to install database software, but you store data
using SQL, the standard database communication language. SQLite is a quick
option for storing and retrieving small amounts of data in a flat file using SQL.
SQLite is not a good option for really huge, complicated databases.
Using Flat Files
Flat files are simple to use, simpler than databases. You don’t need any other
software, such as database software. You just use PHP statements to read
from or write to the file.
Using a flat file requires three steps:
1. Open the file.
2. Write data into the file or retrieve data from the file.
3. Close the file.
These steps are discussed in detail in the following sections.
Accessing files
The first step, before you can write information into or read information from
a file, is to open the file. The following is the general format for the statement
that opens a file:
$fh = fopen(“filename”,”mode”)
The variable, $fh, referred to as a file handle, is used in the statements that
write data to or read data from the open file so that PHP knows which file
to write into or read from. $fh contains the information that identifies the
location of the open file.
You use a mode when you open the file to let PHP know what you intend to
do with the file. Table 12-1 shows the modes you can use.
249 Chapter 12: Storing Data with PHP
Table 12-1 Modes for Opening a File
Mode What it does What happens when the file doesn’t exist
r Read only. If the file does not exist, a warning message
is displayed.
r+ Reading and writing. If the file does not exist, a warning message
is displayed.
w Write only. If the file does not exist, PHP attempts to
create it. If the file exists, PHP overwrites it.
w+ Reading and writing. If the file does not exist, PHP attempts to
create it. If the file exists, PHP overwrites it.
a Append data at the end If the file does not exist, PHP attempts to
of the file. create it.
a+ Reading and appending. If the file does not exist, PHP attempts to
create it.
The filename can be a simple filename (filename.txt), a path to the file
(c:/data/filename.txt), or a URL (http://yoursite.com/filename.txt).
Opening files in read mode
You can open the file file1.txt to read the information in the file with the
following statement:
$fh = fopen(“file1.txt”,”r”);
Based on this statement, PHP looks for file1.txt in the current directory,
which is the directory where your PHP script is located. If the file can’t be
found, a warning message, similar to the following, may or may not be displayed,
depending on the error level set, as described in Chapter 4:
Warning: fopen(file1.txt): failed to open stream: No such
file or directory in d:\test2.php on line 15
Remember, a warning condition does not stop the script. The script continues
to run, but the file doesn’t open, so any later statements that read or
write to the file aren’t executed.
You probably want the script to stop if the file can’t be opened. You need to
do this yourself with a die statement, as follows:
250 Part IV: Common PHP Applications
$fh = fopen(“file1.txt”,”r”)
or die(“Can’t open file”);
As explained in Chapter 8, the die statement stops the script and displays the
specified message.
Opening files in write mode
You can open a file in a specified directory to store information by using the
following type of statement:
$fh = fopen(“c:/testdir/file1.txt”,”w”);
If the file does not exist, it is created in the indicated directory. However, if
the directory doesn’t exist, the directory is not created, and a warning is displayed.
(You must create the directory first, before you try to write a file into
the directory.)
You can check whether a directory exists before you try to write a file into it
by using the following statements:
If(is_dir(“c:/tester”))
{
$fh = fopen(“c:/testdir/file1.txt”,”w”);
}
With these statements, the fopen statement is executed only if the directory
exists and is a directory.
Opening files on another Web site
You can also open a file on another Web site by using a statement such as the
following:
$fh = fopen(“http://janet.valade.com/index.html”,”r”);
You can use a URL only with a read mode, not with a write mode.
Closing a file
To close a file after you have finished reading or writing it, use the following
statement:
fclose($fh);
In this statement, $fh is the file handle variable you created when you
opened the file.
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Writing to a file
After you open the file, you can write into it by using the fwrite statement,
which has the following general format:
fwrite($fh,datatosave);
In this statement, $fh is the file handle that you created when you opened
the file, containing the pointer to the open file, and datatosave is the information
to be stored in the file. The information can be a string or a variable.
For example, you can use the following statements:
$today = date(“Y-m-d”);
$fh = fopen(“file2.txt”,”a”);
fwrite($fh,$today);
fclose($fh);
These statements store the current date in a file called file2.txt. Notice
that the file is opened in append mode. If the file doesn’t exist, it is created,
and the date is written as the first line. If the file exists, the data is added to
the end of the file. In this way, you create a log file, which stores a list of the
dates on which the script is run. The fwrite statement stores exactly what
you send, so the second time these statements are run, file2.txt contains
the following:
2003-04-222003-04-22
You probably want the two dates to be stored on separate lines. To do so, use
the following fwrite statement rather than the previous one:
fwrite($fh,$today”\n”);
With the new line character added, file2.txt contains the following:
2003-04-22
2003-04-22
Be sure to open the file with the a mode if you want to add information to a
file. If you use a write mode, the file is overwritten each time it’s opened.
Reading from a file
You can read from a file by using the fgets statement, which has the following
general format:
$line = fgets($fh)
252 Part IV: Common PHP Applications
In this statement, $fh holds the pointer to the open file. This statement reads
a string until it encounters the end of the line or the end of the file, whichever
comes first, and stores the string in $line. To read an entire file, you keep
reading lines until you get to the end of the file. PHP recognizes the end of the
file, and provides a function feof to tell you when you reach the end of the
file. The following statements read and display all the lines in the file:
while(!feof($fh))
{
$line = fgets($fh);
echo “$line;
}
In the first line, feof($fh) returns TRUE when the end of the file is reached.
The exclamation point negates the condition being tested, so that the while
statement continues to run as long as the end of the file is not reached. When
the end of the file is reached, while stops.
If you use these statements to read the log file created in the preceding section,
you get the following output:
2003-04-22
2003-04-22
As you can see, the new line character is included when the line is read. In
some cases, you don’t want the end of line included. If so, you need to remove
it by using the following statements:
while(!feof($fh))
{
$line = rtrim(fgets($fh));
echo “$line;
}
The rtrim function removes any trailing blank spaces and the new line character.
The output from these statements is as follows:
2003-04-222003-04-22
Reading files piece by piece
Sometimes you want to read strings of a certain size from a file. You can tell
fgets to read a certain number of characters by using the following format:
$line = fgets($fh,n)
This statement tells PHP to read a string that is n-1 characters long until it
reaches the end of the line or the end of the file.
253 Chapter 12: Storing Data with PHP
For example, you can use the following statements:
while(!feof($fh))
{
$char4 = fgets($fh,5);
echo “$char4\n”;
}
These statements read each four-character string until the end of the file. The
output is as follows:
2003
-04-
22
2003
-04-
22
Notice that there is a new line at the end of each line of the file.
Reading a file into an array
It’s often handy to have the entire file in an array. You can do that with the
following statements:
$fh = fopen(“file2.txt”,”r”);
while(!feof($fh))
{
$content[] = fgets($fh);
}
fclose($fh);
The result is the array $content with each line of the file as an element of
the array. The array keys are numbers.
PHP provides a shortcut function for opening a file and reading the entire
contents into an array, one line in each element of the array. The following
statement produces the same results as the preceding five lines:
$content = file(“file2.txt”);
The statement opens file2.txt, puts each line into an element of the array
$content, and then closes the file.
The file function can slow down your script if the file you’re opening is really
large. How large depends on the amount of available computer memory. If
your script seems slow, try reading the file with fgets rather than file and
see if that speeds up the script.
254 Part IV: Common PHP Applications
You can direct the file function to automatically open files in your include
directory (described in Chapter 
by using the following statement:
$content = file(“file2.txt”,1);
The 1 tells PHP to look for file2.txt in the include directory rather than in
the current directory.
Reading a file into a string
Sometimes it’s useful to put the entire contents of a file into one long string.
For example, you may want to send the file contents in an e-mail message.
PHP provides a function for reading a file into a string, as follows:
$content = file_get_contents(“file2.txt”,1);
The file_get_contents function works the same as the file function,
except that it puts the entire contents of the file into a string rather than an
array. After this statement, you can echo $content as follows:
echo $content;
The output is the following:
2003-04-22
2003-04-22
The output appears on separate lines because the end of line characters are
read and stored as part of the string. Thus, when you echo the string, you
also echo the end of line characters, which start a new line.
The file_get_contents function was introduced in version 4.3.0. It isn’t
available in older versions of PHP.
Exchanging data with other programs
Flat files are particularly useful for providing information to other programs
or reading information into PHP from other programs. Almost all software has
the ability to read information from flat files or write information into flat files.
For example, by default your word processor saves your documents in its own
format, which only the word processor can understand. However, you can
choose to save the document in text format instead. The text document is a
flat file containing text that can be read by other software. Your word processor
can also read text files, even ones that were written by other software.
255 Chapter 12: Storing Data with PHP
When your PHP script saves information into a text file, the information can be
read by any software that has the capability of reading text files. For example,
any text file can be read by most word processing software. However, some
software requires a specific format in the text file. For example, an address
book software application may read data from a flat file but require the information
to be in specified locations — for example, the first 20 characters in a
line are read as the name, and the second 20 characters are read as the street
address, and so on. You need to know what format the software requires in
a flat file. Then write the flat file in the correct format in your PHP script by
using fwrite statements, as discussed in the section “Writing to a file,” earlier
in this chapter.
A CSV (comma-separated values) file — also called a comma-delimited file —
is a common format used to transfer information between software programs.
A CSV file is used to transfer information that can be structured as a table,
organized as rows and columns. For example, spreadsheet programs organize
data as rows and columns and can read and write CSV files. A CSV file is also
often used to transfer data between different database software, such as
between MySQL and MS Access. Many other software programs can read and
write data in CSV files.
A CSV file is organized with each row of the table on a separate line in the file,
and the columns in the row are separated by commas. For example, an address
book can be organized as a CSV file as follows:
John Smith,1234 Oak St.,Big City,OR,99999
Mary Jones,5678 Pine St.,Bigger City,ME,11111
Luis Rojas,1234 Elm St.,Biggest City,TX,88888
Excel can read this file into a table with five columns. The comma signals the
end of one column and the start of the next. Outlook can also read this file
into its address book. And many other programs can read this file.
The following PHP statements create the CSV file:
$address[] = “John Smith,1234 Oak St.,Big City,OR,99999”;
$address[] = “Mary Jones,5678 Pine St.,Bigger City,ME,11111”;
$address[] = “Luis Rojas,1234 Elm St.,Biggest City,TX,88888”;
$fh = fopen(“addressbook.txt”,”a”);
for ($i=0;$i<3;$i++)
{
fwrite($fh,$address[$i].”\n”);
}
fclose($fh);
PHP can read the CSV file by using either the file or the fgets function, as
described in the section “Reading a file into an array,” earlier in this chapter.
However, PHP provides a function called fgetcsv that is designed specifically
to read CSV files. When you use this function to read a line in a CSV file, the
line is stored in an array, with each column entry in an element of the array.
256 Part IV: Common PHP Applications
For example, you can use the function to read the first line of the address
book CSV file, as follows:
$address = fgetcsv($fh,1000);
In this statement, $fh is the file handle, and 1000 is the number of characters
to read. To read an entire line, use a number of characters that is longer than
the longest line. The result of this statement is an array as follows:
$address[0] = John Smith
$address[1] = 1234 Oak St.
$address[2] = Big City
$address[3] = OR
$address[4] = 99999
The CSV file works well for transferring data in many cases. However, if a
comma is part of the data, commas can’t be used to separate the columns.
For example, suppose one of data lines is as follows:
Smith Company, Inc.,1234 Fir St.,Big City,OR,99999
The comma in the company name would divide the data into two columns —
Smith Company in the first and Inc. in the second — making six columns
instead of five. When the data contains commas, you can use a different character
to separate the columns. For example, tabs are commonly used to separate
columns. This file is called a TSV file or a tab-delimited file. You can write
a tab-delimited file by storing “\t” in the output file rather than a comma.
You can read a file containing tabs by specifying the column separator in the
statement, as follows:
$address = fgetcsv($fh,1000,”\t”);
You can use any character to separate columns.
The script in Listing 12-1 contains a function that converts any CSV file into a
tab-delimited file.
Listing 12-1: A Script That Converts a CSV File into a Tab-Delimited File
<?php
/* Script name: Convert
* Description: Reads in a CSV file and outputs a
* tab-delimited file. The CSV file must have a .
* CSV extension.
*/
$myfile = “testing”; #7
function convert($filename) #8
(continued)
257 Chapter 12: Storing Data with PHP
Listing 12-1 (continued)
{
if(@$fh_in = fopen(“{$filename}.csv”,”r”)) #10
{
$fh_out = fopen(“{$filename}.tsv”,”a”); #12
while(!feof($fh_in)) #13
{
$line = fgetcsv($fh_in,1024); #15
if($line[0] == “”) #16
{
fwrite($fh_out,”\n”);
}
else { #20
fwrite($fh_out,implode($line,”\t”).”\n”); #21
}
}
fclose($fh_in);
fclose($fh_out);
}
else { #27
echo “File doesn’t exist\n”;
return FALSE;
}
echo “Conversion completed!\n”;
return TRUE; #32
}
convert($myfile); #34
?>
Listing 12-1 has numbers at the end of some lines. The following points refer
to the line numbers in the listing:
Line 7: This line defines the filename as testing.
Line 8: This line defines a function named convert() with one parameter,
$filename.
Line 10: This line opens a file that has the filename that was passed to
the function with a .csv extension. The file is opened in read mode. If the
file is opened successfully, the conversion statements in the if block
are executed. If the file is not found, the else block beginning on line 27
is executed.
Line 12: This line opens a file that has the filename that was passed to
the function with a .tsv extension. The file is opened in append mode.
The file is in the current directory in this script. If the file is in another
directory where you think there is any possibility the file might not open
in write mode, use an if statement here to test where the file opened
and perform some action if it did not.
Line 13: This line starts a while loop that continues to the end of the file.
258 Part IV: Common PHP Applications
Line 15: This statement reads one line from the input file into the array
$line. Each column entry is stored in an element of the array.
Line 16: This statement tests whether the line from the input file has any
text on it. If the line doesn’t have any text, a new line character is stored
in the output file. Thus, any empty lines in the input file are stored in the
output file.
Line 20: If the line from the input file is not empty, it’s converted to a
tab-delimited format and written into the output file.
Line 21: This statement converts the line and writes it to the output file
in one statement. The implode function converts the array $line into a
string, with the elements separated by a tab.
Line 27: This else block executes when the input file can’t be found. An
error message is echoed, and the function returns FALSE.
Line 32: The function has completed successfully, so it returns TRUE.
Line 34: This line calls the function, passing a filename to the function in
the variable $myfile.
Working with Databases
If you need to store complex information, keep the information very secure,
or handle many users accessing the data at once, a database is much better
than a flat file for long-term storage. Also, if you already know and use database
software, it’s almost as simple to use a database as a flat file.
Understanding database software
A database is an electronic file cabinet that stores information in an organized
manner so that you can find it when you need it. A database can be small,
with a simple structure, such as a database containing the names, addresses,
and phone numbers of all your friends. Or a database can be huge with an
extremely complex structure, such as the database Amazon must have to
hold all its information.
Technically, the term database refers to the file or group of files that holds the
actual data. The data is accessed by using a set of programs called a Database
Management System (DBMS). Almost all DBMSs these days are Relational
Database Management Systems (RDBMSs), in which data is organized and
stored in a set of related tables.
259 Chapter 12: Storing Data with PHP
One of PHP’s strengths is its support for many different DBMSs. PHP supports
over 20 databases. It supports the following popular RDBMSs, as well as others
that are less well known:
IBM DB2
Informix
Ingres
Microsoft SQL Server (MS SQL)
mSQL
MySQL
Oracle
PostgreSQL
Sybase
In addition, PHP offers support for ODBC, which stands for the Open Database
Connectivity standard, a standard database access method developed by
Microsoft. Many DBMSs understand ODBC, particularly Windows DBMSs. Using
ODBC support in PHP, you can access some databases that are not specifically
supported, such as DB2 and Access. Also, you can use ODBC to access several
different databases with the same code. To use ODBC to communicate with a
database, the database needs to have an ODBC driver installed. See the documentation
for your database to find out how to install ODBC support for your
database.
If you currently have a database set up and know how to use it, you can
undoubtedly store and retrieve data from your existing database by using
PHP scripts. If you don’t have an existing database, you need to choose one.
Selecting and installing a database is independent of PHP. You install the database,
make sure it’s working, and learn to use it. After your database is working,
you can store and retrieve data with PHP scripts.
Choosing a RDBMS depends on your needs. The RDBMS that is right for you
may not be the best option for someone else. You need to research your
options and choose the one with the characteristics that suit your situation.
You may need to consider some of the following issues:
Cost: The cost of the RDBMS software ranges from free to quite pricey.
MySQL, mSQL, and PostgreSQL are open source software, meaning they’re
free. Other RDBMSs, such as Sybase, MS SQL Server, and Oracle, are commercial
software with prices that range from moderate to astronomical.
260 Part IV: Common PHP Applications
Features: The features provided by an RDBMS vary. For example, mSQL
has a small set of features, but this may be enough for some purposes.
On the other hand, Oracle can do everything but drive your car. In general,
the more features the RDBMS has, the more computer resources it
requires and the higher its cost. Therefore, you may not want to install
software with a huge feature set that you don’t need.
Resources: Some RDBMSs require more resources, such as disk space and
memory, than others. For example, mSQL is very small and lightweight,
requiring very little overhead. MySQL was also developed to be small.
On the other hand, Oracle, depending on which products and tools you
install, can require many resources.
Support: Commercial software and open source software provide support
differently:
• Commercial: Commercial software provides a method for customers
to get technical support from the company that sold them the software.
Sometimes customers have to pay for the technical support
or wait in phone queues, but the company answers their questions
and assists with troubleshooting.
• Open source: Open source software does not provide a direct phone
line to a software company. Open source software is supported by
the community of users. E-mail lists and forums offer access to many
people who are using the software and who are willing to answer
questions and assist each other with problems. Sometimes asking
a question on an e-mail list gets you an answer faster than phoning
a technical-support phone number at a software company.
After you choose which database you’re going to use, you need to install
the database software and figure out how to use it. You need to know how to
design and create a database that you can then access from a PHP script. In
general, a database has two parts: a structure to hold the data and the data
itself.
The structure consists of the database itself and tables within the database
that hold the data. You need to design the database structure before you can
store data in it. RDBMS tables are organized like other tables you’re used to —
in rows and columns. For example, suppose you want to provide an online catalog,
containing all your products, so users can see what you have and place
orders. You create a database called Catalog. In the Catalog database, you
create a table called Product that contains all your products. The Product table
has a different product in each row. The columns of the row contain information
about each product. For example, if the product is a shirt, each row of the
table contains information about a different shirt you sell. The columns contain
information about the shirt, such as the name of the shirt (T-shirt, dress
shirt, polo shirt, and so on), the description, the size, the color, and so on.
261 Chapter 12: Storing Data with PHP
When you create a table, you give each column a name, called the field name.
For your Product table containing shirts, you name the columns as follows:
Type
Description
Size
Color
Price
Your Catalog database can have other tables in it, such as a table containing
shipping costs and a table containing sales tax information.
In addition to the database design and creation, you need to understand the
security used by your RDBMS. One of the advantages of databases is the security
provided for the data, but the security makes storing and retrieving data
more complicated. The RDBMS doesn’t allow just anyone to get data from your
database. You need to have a valid account name and password before you
can use the database. If you’re using a database on a Web hosting company,
those folks need to provide you with a valid account and password. If you’re
installing the database software yourself, you need to understand how to
administer the accounts.
After you have designed and created the database structure, you can add
data to the tables and retrieve stored data from the tables. PHP makes data
storage and retrieval quite simple.
Understanding database support in PHP
PHP communicates with databases by using functions designed specifically
to interact with databases. PHP includes a set of functions for each database
it supports. For example, to communicate with MySQL 4.0 or earlier, you use
functions such as mysql_connect() and mysql_query() and to communicate
with MySQL 4.1 or later, you use functions such as mysqli_connect()
and mysqli_query(). To communicate with Sybase, you use functions such
as sybase_connect() and sybase_query().
By default, PHP includes support for ODBC. For database support other than
ODBC, you must add support for the database you plan to use. If you’re using
a Web hosting company, those folks must provide the database support. If
you’re running your Web site on your own computer, you need to add database
support to PHP. You can include database support by using the methods
described in the following sections.
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Setting up database support in Unix/Linux/Mac
Support for a database is an installation option that is included in the configure
step during installation. Appendix A includes a section that discusses
the installation options. For example, to include support for mSQL, use the
following command line options in the configuration step during installation:
./configure –with-msql=/usr/msql
Table 12-2 shows many of the database installation options available. If the
database is installed in the default location, you don’t need to include the
DIR parameter. You can use the option without the parameter, as follows:
./configure –with-msql
Table 12-2 PHP Database Installation Options
Database Installation Option Default DIR
IBM DB2 with-ibm-db2=DIR /home/db2inst1/sqllib
Informix with_informix=DIR No default
Ingres II with-ingres=DIR /II/ingres
mSQL with-msql=DIR /usr/local/Hughes
MySQL 4.0 or earlier with-mysql=DIR /usr/local/mysql
MySQL 4.1 or greater with-mysqli=DIR No default. DIR must be the
path to the file mysql_
config that is installed with
MySQL 4.1 or greater.
Oracle 7 and newer with-oci8 Default DIR is contained in
versions the environmental variable,
ORACLE_HOME
Earlier versions of with-oracle=DIR Default DIR is contained in
Oracle the environmental variable,
ORACLE_HOME
PostgreSQL with-pgsql=DIR /usr/local/pgsql
Sybase with-sybase=DIR /home/sybase
Sybase-CT with-sybase-ct=DIR /home/sybase
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After you compile PHP using the appropriate installation option, you can check
that database support was correctly activated with the phpinfo function. The
database support and settings appears in the output from phpinfo.
Setting up database support in Windows
Enabling PHP support for a database in Windows requires two steps:
1. Copy the dll (Dynamic Link Library) file for the database into the
main directory.
2. Activate the database support.
After performing the steps, as described below, you can use the phpinfo
function to check that the database support has been activated. Information
and settings for the database are displayed in the output from phpinfo.
Copying the dll
The dlls are included in the zip file you download from the PHP Web site.
Downloading and installing PHP manually from the zip file is described in
Appendix A. After installing manually, a directory called ext is in the directory
where PHP is installed. The path will be something like c:\php\ext, and
the dlls for the databases are in this directory.
Copy the dll you need into the main directory where PHP is installed, such as
c:\php. For example, to add support for PostgreSQL to PHP on a Windows
2000 system, copy c:\php\ext\php_pgsql.dll into the main directory
where PHP is installed. To do this, CD into c;\php\ext and type:
copy php_pgsql.dll
If you used the installer to install PHP, the database dlls were not downloaded.
You need to download the zip file, as described for installing PHP manually.
Then unzip the file, find the appropriate dll, and copy it into the system
directory.
Activating the database support
Database support is activated in the php.ini file. Look for a list of statements
that have the following form:
;extension=php_pgsql.dll
;extension=php_msql.dll
This list includes a statement for every database that is supported. Notice
the semicolon at the beginning of each line. The semicolon is the comment
character in the php.ini file, so the statements in the list are comments and
are not active. Find the statement for the database support you need and
then remove the semicolon from the statement for the database support you
want to activate, as in the following example
264 Part IV: Common PHP Applications
extension=php_pgsql.dll
This statement activates PostgreSQL support. After you save the php.ini file,
you may need to restart your Web server before the database support goes
into effect.
If you activate the database support line in php.ini, but haven’t copied the
dll into the main directory, you will see an error message similar to the following
when you try to run a PHP script:
Unknown(): Unable to load dynamic library ‘php_pgsql.dll’.
The specified module could not be found.
If you perform both steps correctly (copy the dll into the main directory and
activate the correct line in php.ini), but the database software isn’t
installed, you will get an error message similar to the following when you try
to run a PHP script:
The dynamic link library msql.dll could not be found in the
specified path
For MS SQL users only: You need to install the MS SQL Server Client Tools,
as well as the database server. Microsoft provides these tools on the CD.
For MySQL users only: Be sure you use the correct dll: php_mysql.dll for
MySQL 4.0 or earlier or php_mysqli.dll for MySQL 4.1 or later.
Communicating with your database
Most database software understands SQL (Structured Query Language), a
computer language you use to communicate with a database. You send an SQL
statement, called a query, to the RDBMS that tells it what you want to do. SQL
queries can instruct the RDBMS to create a database, create tables in a database,
store data, retrieve data, delete data, and perform many other actions.
Although most databases understand SQL, there may be differences in the
SQL you can use with different databases. For example, mSQL understands a
limited set of SQL queries, but Oracle and Sybase each have an extended set
of SQL queries they understand, beyond the standard SQL.
A complete description of SQL is beyond the scope of this book. If you’re
using MySQL as your database, you may want to look at my other book, PHP
& MySQL For Dummies (Wiley Publishing, Inc.). A description of the SQL you
need to work with databases is contained in this book. Or, for a complete
description of SQL and all its capabilities and features, see SQL For Dummies,
5th Edition, by Allen Taylor (Wiley Publishing, Inc.).
265 Chapter 12: Storing Data with PHP
Although I do not discuss SQL in detail, I will describe a couple of simple SQL
queries so that I can use some real examples in this book to show you how to
use your database. To get data from your database, you can use the following
query:
SELECT * FROM tablename
This query retrieves all the data that is contained in the table. The