Extension structure
PHP Manual

Basic constructs

C is a very low-level language by modern definitions. This means that it has no built-in support for many features that PHP takes for granted, such as reflection, dynamic module loading, bounds checking, threadsafe data management and various useful data structures including linked lists and hash tables. At the same time, C is a common denominator of language support and functionality. Given enough work, none of these concepts are impossible; the Zend Engine uses them all.

A lot of effort has gone into making the Zend API both extensible and understandable, but C forces certain necessary declarations upon any extension that to an inexperienced eye seem redundant or plain unnecessary. All of those constructs, detailed in this section, are "write once and forget" in Zend Engine 2 and 3. Here are some excerpts from the pre-generated php_counter.h and counter.c files created by PHP 5.3's ext_skel, showing the pre-generated declarations:

Note: The astute reader will notice that there are several declarations in the real files that aren't shown here. Those declarations are specific to various Zend subsystems and are discussed elsewhere as appropriate.

extern zend_module_entry counter_module_entry;
#define phpext_counter_ptr &counter_module_entry

#ifdef PHP_WIN32
#    define PHP_COUNTER_API __declspec(dllexport)
#elif defined(__GNUC__) && __GNUC__ >= 4
#    define PHP_COUNTER_API __attribute__ ((visibility("default")))
#    define PHP_COUNTER_API

#ifdef ZTS
#include "TSRM.h"
#include "config.h"

#include "php.h"
#include "php_ini.h"
#include "ext/standard/info.h"
#include "php_counter.h"

/* ... */


Extension structure
PHP Manual