How you can build a "Hello World" PHP extension in five steps

Taken from https://stackoverflow.com/questions/3632160/how-to-make-a-php-extension

A Debian based OS is required, because we need to fetch some tools and dependencies with apt-get.

Step 1 - Setup Build Environment / Requirements

A PHP Extension is compiled C code. We need a shell (should already be installed), an editor (your choice), a compiler (here we'll use GCC), PHP itself and PHP development dependencies for the build.

sudo apt-get install build-essential php7.0 php7.0-dev

Step 2 - Config

We need to describe our extension and the files forming it in a basic configuration file:

File: config.m4

PHP_ARG_ENABLE(php_helloworld, Whether to enable the HelloWorldPHP extension, [ --enable-helloworld-php Enable HelloWorldPHP])

if test "$PHP_HELLOWORLD" != "no"; then
    PHP_NEW_EXTENSION(php_helloworld, php_helloworld.c, $ext_shared)
fi

As you can see, the NEW_EXTENSION contains a C file: php_helloworld.c.

Step 3 - Code

Let's create the C code for our extension.

Firstly, we create a header file:

php_helloworld.h

// we define Module constants
#define PHP_HELLOWORLD_EXTNAME "php_helloworld"
#define PHP_HELLOWORLD_VERSION "0.0.1"

// then we declare the function to be exported
PHP_FUNCTION(helloworld_php);

Secondly, we create the source file:

php_helloworld.c

// include the PHP API itself
#include <php.h>
// then include the header of your extension
#include "php_helloworld.h"

// register our function to the PHP API 
// so that PHP knows, which functions are in this module
zend_function_entry helloworld_php_functions[] = {
    PHP_FE(helloworld_php, NULL)
    {NULL, NULL, NULL}
};

// some pieces of information about our module
zend_module_entry helloworld_php_module_entry = {
    STANDARD_MODULE_HEADER,
    PHP_HELLOWORLD_EXTNAME,
    helloworld_php_functions,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    PHP_HELLOWORLD_VERSION,
    STANDARD_MODULE_PROPERTIES
};

// use a macro to output additional C code, to make ext dynamically loadable
ZEND_GET_MODULE(helloworld_php)

// Finally, we implement our "Hello World" function
// this function will be made available to PHP
// and prints to PHP stdout using printf
PHP_FUNCTION(helloworld_php) {
    php_printf("Hello World! (from our extension)\n");
}

Step 4 - Build

Now, we are ready to build the extension.

First we prepare the build environment for a PHP extension:

phpize

Then we configure the build and enable our extension:

./configure --enable-php-helloworld

Finally, we can build it:

make
sudo make install

Step 5 - Test

To test our PHP extension, lets load the helloworld_php.so extension file and execute our function helloworld_php():

php -d extension=php_helloworld.so -r 'helloworld_php();'

Done :)