PHP Extensions Made Eldrich: Hello, World!

This is part 2 of a 4-part tutorial on writing PHP extensions:

  1. Setting Up PHP – compiling PHP for extension development
  2. Hello, world! – your first extension
  3. Working with the API – the PHP C API
  4. Classes – creating PHP objects in C

First we need to think of a name for our extension. I’ve been reading some H.P. Lovecraft, so let’s call it “rlyeh”.

For our first extension, we’ll create a new function, cthulhu(). When we call cthulhu() (tee hee), PHP will print “In his house at R’lyeh dead Cthulhu waits dreaming.”

Cheat Sheet

If you don’t want to copy/paste all of the code, you can clone the Github repo for this tutorial and check out sections as you go.

$ git clone git://

This part of the tutorial (Hello, world!) is the master branch. Stating in part 3, each “unit” has a branch: <branchname> at the beginning of the section. You can checkout this branch if you want to see the code example in context.

For example, if you see branch: oop, you’d do:

$ git checkout -b oop origin/oop

Then you can compare what you’re doing to the “ideal” example code.

Setting Up

Create a directory for your PHP extension, named “rlyeh”. This is where all of the source code for your extension will live.

$ mkdir rlyeh
$ cd rlyeh

A PHP extension consists of at least three files:

  1. “config.m4”, which contains compilation instructions for PHP
  2. “php_extname.c”: source code
  3. “php_extname.h”: a header file

Creating a config.m4 file is wholly lacking in interest, so just cut/paste the one below.

dnl lines starting with "dnl" are comments

PHP_ARG_ENABLE(rlyeh, whether to enable Rlyeh extension, [  --enable-rlyeh   Enable Rlyeh extension])

if test "$PHP_RLYEH" != "no"; then

  dnl this defines the extension
  PHP_NEW_EXTENSION(rlyeh, php_rlyeh.c, $ext_shared)

  dnl this is boilerplate to make the extension work on OS X
  case $build_os in
    AC_MSG_CHECKING([whether to compile for recent osx architectures])
    CFLAGS="$CFLAGS -arch i386 -arch x86_64 -mmacosx-version-min=10.5"
    AC_MSG_CHECKING([whether to compile for every osx architecture ever])
    CFLAGS="$CFLAGS -arch i386 -arch x86_64 -arch ppc -arch ppc64"


If you want to call your extension something else, global replace “rlyeh” with your extension’s name.

Now for the actual extension: create a file called php_rlyeh.c with the following content:

// include PHP API
#include <php.h>
// header file we'll create below
#include "php_rlyeh.h"
// define the function(s) we want to add
zend_function_entry rlyeh_functions[] = {
  PHP_FE(cthulhu, NULL)
// "rlyeh_functions" refers to the struct defined above
// we'll be filling in more of this later: you can use this to specify
// globals, php.ini info, startup and teardown functions, etc.
zend_module_entry rlyeh_module_entry = {
// install module
// actual non-template code!
PHP_FUNCTION(cthulhu) {
    // php_printf is PHP's version of printf, it's essentially "echo" from C
    php_printf("In his house at R'lyeh dead Cthulhu waits dreaming.\n");

That’s a whole lotta template, but it’ll make more sense as you go along.

Learning PHP extension programming is sort of like learning Java as your first programming language: “type ‘public static void main’.” “Why? What does that even mean?” “It doesn’t matter, you’ll learn about it later.”

You also have to make a header file, to declare the cthulhu function as well as the two extension info macros used in php_rlyeh.c (PHP_RLYEH_EXTNAME and PHP_RLYEH_VERSION).

Create a new file, php_rlyeh.h, and add a couple of lines:

#define PHP_RLYEH_EXTNAME "rlyeh"
#define PHP_RLYEH_VERSION "0.01"

You can change the version whenever you do a new release. It can be any string. It’s displayed when you do:

$ php --ri rlyeh

(once the extension is installed).

Speaking of, now all that’s left is to compile and install. Make sure that your custom-compiled-PHP is first in your PATH. If it isn’t, put it there before doing the rest of the install.

$ echo $PATH
$ phpize
Configuring for:
PHP Api Version:         20090626
Zend Module Api No:      20090626
Zend Extension Api No:   220090626
$ ./configure
# lots of checks...
$ make
# compile...

Build complete.
Don't forget to run 'make test'.

$ make install
Installing shared extensions:     $PHPDIR/install-debug-zts/lib/php/extensions/debug-zts-20090626/

Now, add your extension to your php.ini file. PHP is probably expecting a php.ini file in the lib/ subdirectory of your install directory ($PHPDIR/install-debug-zts/lib/php.ini). It probably doesn’t exist yet, so create a new php.ini file with one line:

Now you should be able to use your function from PHP without importing, loading, or requiring anything. Do:

$ php -r 'cthulhu();'
In his house at R'lyeh dead Cthulhu waits dreaming.

Your first PHP extension is working!

Next up: a deep dive into the PHP API.

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