What
is a PHP extension?
A PHP extension, in the most basic of terms,
is a set of instructions (i.e. code) that is designed to add
functionality to PHP. For example, the widely used GD library
(used for the creation of dynamic images) is an extension. This
library added new functionality by allowing PHP to generate
images on the fly. Another example is the MySQL extension, which
allows us to connect to and work with MySQL databases.
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What are PHP extensions needed for? There are several reasons
why extensions are needed. One of them, as stated above, is
to add new functionality to PHP. For instance, where would we
be today if someone did not add the functionality to work with
MySQL? Where will we be tomorrow if someone does not add the
functionality to work with tomorrow’s databases or tomorrow's
technologies? As PHP continues to grow, it is likely that new
"features" will be required by the ever-growing number of web
developers. Some of the new features will be popular enough
to be added to the official distribution, while others will
not. Either way, those extensions will serve their creators
well.
On the other hand, we might use PHP extensions to improve the
efficiency and speed of our programs. Some processor intensive
functions might be better coded as an extension rather than
straight PHP code. Since extensions are written in C (more on
the actual coding later), they will work much faster than straight
PHP code too.
Another possible reason to employ extensions is to reuse frequently
utilized code. Instead of moving the same old functions from
project to project, you could place them all in one extension
and allow all your projects to utilize that extension.
How do I develop
my own extensions?
Before this question can be answered, we
must look at the different "types" of extensions available.
Extensions come in three different flavors: Zend engine extensions,
built-in extensions and external extensions.
Zend Engine extensions are extensions that are implemented right
into the engine itself. For those of you who do not know, the
Zend engine is what PHP is built on. It is the engine that parses,
interprets and executes your PHP scripts. Changing the engine
itself will change the way PHP works. Anything that will affect
the language itself or its features is added to the Zend engine;
this includes if statement evaluation, object orientation, mathematical
expressions evaluation, etc.
Although extending the engine is possible, it's not recommenced
for reasons such as incompatibility with servers that run the
officially distributed engine. In other words, not too many
server administrators will agree to use an unofficial version
of the Zend engine.
Built-in extensions are extensions that are compiled right into
PHP and are loaded with the PHP processes. The advantages of
this method are: programmers aren't required to load extensions
manually, and no extension files are required (since it is compiled
right into the PHP binary itself). The disadvantages, on the
other hand, are: any changes to the extension will require a
complete re-compilation of the PHP binary itself, and the size
of the binary will grow with each new extension (as will the
amount of memory it will consume).
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External extensions are extensions that are manually added during
run time. All the functionality of the extension will be available
to the script that loaded it. When the script ends, the extension
is released and the memory is freed. As you might guess, the
advantages are: only the extension itself needs to be re-compiled
after any changes and a small PHP binary. Also, you don’t provide
the functionality of your extension to scripts that do not require
it. And, as always, where advantages go, disadvantages follow:
extensions are loaded during run time, a process that takes
time, and the programmer must remember to load the extension
since it is not automatically available.
Although loading external extensions each time the script is
executed takes time, it is fairly quick. I personally do not
feel any speed differences when I load my external extensions.
Of course, if the site receives heavy traffic, a speed difference
might be apparent and built-in extensions might be the most
appropriate solution. Nevertheless, in these articles we will
develop an external extension. Note that the difference between
built-in extensions and external extensions – code wise – is
virtually nonexistent.
Setting up
our Development environment
In this tutorial I will use Microsoft's Visual C++ 6.0 compiler.
Compiling extensions on Unix / Linux systems is fairly well
documented. On windows, however, this isn't the case.
The first thing you must do is download the PHP source code
distribution, php-4.2.1.tar.gz, from the PHP web site.
At the time of writing the latest version of PHP was 4.2.1
Once the source code is downloaded, create a directory where
you will keep the source code and where you will hold the sources
of your extensions. In my case, this will be D:devarticlesphp-devphp-4.2.1.
Extract the contents of php-4.2.1.tar.gz into that directory
(I used WinRAR to extract the file).
Next, move into the ext directory, which is D:devarticlesphp-devphp-4.2.1ext
in my case. There you will see all of the different extensions
that are currently being distributed with PHP. Any time during
your coding process when something does not work, it is a good
idea to just open an extension and read through the source code.
Moving right along, open your MS Visual Studio and make sure
no other projects or files are open. Under the File menu, choose
New and from the list of wizards choose the "Win32 Dynamic-Link
Library". All PHP extensions under windows must be in form of
a DLL, thus it is imperative to choose the right type of project.
Choosing anything different will result in ugly and indecipherable
linker errors (If you've ever worked with Visual C++, no doubt
you are familiar with the cryptic messages the compiler throws
at you).
Now, for the location. Enter – or rather browse to – the extension
subdirectory in your PHP development directory. For the project
name enter "devarticles" and this should be appended automatically
to your location.
Click the OK button. On the next menu choose "An empty DLL project"
and click the finish button. A new window should open up and
show you all the information relating to the project; click
the OK button again. Click
here to continue the article. |
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