“If the code and the comments disagree, then both are probably wrong.”–
Norm Schryer
One of the main reasons for PHP’s success is the large amount of available
extensions. No matter what a web developer might need, he’ll most probably
find it in the PHP distribution, including extensions that support various
databases, graphic file formats, compression, XML technologies, and lots
more.
The big breakthrough for PHP happened in PHP 3 with the introduction
of the extension API, which allowed the PHP development community to
easily extend PHP with dozens of extensions. Today, two versions later, the
API still very strongly resembles what existed in PHP 3. The idea was to hide
the internals of PHP and the scripting engine itself as much as possible from
the extension writer, and only require him to be proficient in the API itself.
There are two main reasons for writing your own PHP extension. The
first is if you need PHP to support a technology it doesn’t support yet. This
usually involves wrapping some kind of existing C library to give it an inter-
face from PHP. For example, if a new database called FooBase made it to the
market, you’d need to create a PHP extension which allows you to interface
with FooBase’s C library from PHP. This work would only have to be done by
one person and could later be shared with the whole PHP community (if you’d
want to). The second, less common, reason is if you need to write some of your
business logic in C for performance or functionality reasons.
If both of these reasons aren’t relevant to you and you don’t feel adven-
turous, you can probably skip this chapter.
This chapter teaches you how to write relatively simple PHP extensions
with a subset of the extension API. It covers enough material for the majority
of developers who want to write custom PHP extensions. One of the best ways
of learning a programming subject is by doing something extremely simple, which is the route this chapter takes. Once you know the basics, you’ll be able
to easily enrich yourself by reading documentation on the web, the source
code, or participating in discussions on mailing lists and newsgroups. There-
fore, this chapter concentrates on getting you started. It makes use of a UNIX
script called ext_skel, which creates skeleton extensions from a function defi-
nition file describing the extension’s interface. For this reason, you will need to
use UNIX to create the skeleton. Windows developers may use the Windows
ext_skel_win32.php alternative to ext_skel. However, the instructions in this
chapter referring to building PHP with your extensions only cover the UNIX
build system. All the API explanations in this chapter are relevant to both
UNIX and Windows extensions.
After you finish reading this chapter, you will have learned how to
Create a simple extension with business logic.
Create a wrapper extension for a C library, specifically some of the
standard C file operation functions such as fopen().