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Declaration of the Zend Function Block

Now that you have declared the functions to be exported, you also have to introduce them to Zend. Introducing the list of functions is done by using an array of zend_function_entry. This array consecutively contains all functions that are to be made available externally, with the function's name as it should appear in PHP and its name as defined in the C source. Internally, zend_function_entry is defined as shown in Example 31-1.

Example 31-1. Internal declaration of zend_function_entry.

typedef struct _zend_function_entry {
    char *fname;
    void (*handler)(INTERNAL_FUNCTION_PARAMETERS);
    unsigned char *func_arg_types;
} zend_function_entry;

EntryDescription
fname Denotes the function name as seen in PHP (for example, fopen, mysql_connect, or, in our example, first_module).
handler Pointer to the C function responsible for handling calls to this function. For example, see the standard macro INTERNAL_FUNCTION_PARAMETERS discussed earlier.
func_arg_types Allows you to mark certain parameters so that they're forced to be passed by reference. You usually should set this to NULL.

In the example above, the declaration looks like this: 
zend_function_entry firstmod_functions[] =
{
    ZEND_FE(first_module, NULL)
    {NULL, NULL, NULL}
};
You can see that the last entry in the list always has to be {NULL, NULL, NULL}. This marker has to be set for Zend to know when the end of the list of exported functions is reached.

Note: You cannot use the predefined macros for the end marker, as these would try to refer to a function named "NULL"!

The macro ZEND_FE (short for 'Zend Function Entry') simply expands to a structure entry in zend_function_entry. Note that these macros introduce a special naming scheme to your functions - your C functions will be prefixed with zif_, meaning that ZEND_FE(first_module) will refer to a C function zif_first_module(). If you want to mix macro usage with hand-coded entries (not a good practice), keep this in mind.

Tip: Compilation errors that refer to functions named zif_*() relate to functions defined with ZEND_FE.

Table 31-2 shows a list of all the macros that you can use to define functions.

Table 31-2. Macros for Defining Functions

Macro NameDescription
ZEND_FE(name, arg_types) Defines a function entry of the name name in zend_function_entry. Requires a corresponding C function. arg_types needs to be set to NULL. This function uses automatic C function name generation by prefixing the PHP function name with zif_. For example, ZEND_FE("first_module", NULL) introduces a function first_module() to PHP and links it to the C function zif_first_module(). Use in conjunction with ZEND_FUNCTION.
ZEND_NAMED_FE(php_name, name, arg_types) Defines a function that will be available to PHP by the name php_name and links it to the corresponding C function name. arg_types needs to be set to NULL. Use this function if you don't want the automatic name prefixing introduced by ZEND_FE. Use in conjunction with ZEND_NAMED_FUNCTION.
ZEND_FALIAS(name, alias, arg_types) Defines an alias named alias for name. arg_types needs to be set to NULL. Doesn't require a corresponding C function; refers to the alias target instead.
PHP_FE(name, arg_types) Old PHP API equivalent of ZEND_FE.
PHP_NAMED_FE(runtime_name, name, arg_types) Old PHP API equivalent of ZEND_NAMED_FE.

Note: You can't use ZEND_FE in conjunction with PHP_FUNCTION, or PHP_FE in conjunction with ZEND_FUNCTION. However, it's perfectly legal to mix ZEND_FE and ZEND_FUNCTION with PHP_FE and PHP_FUNCTION when staying with the same macro set for each function to be declared. But mixing is not recommended; instead, you're advised to use the ZEND_* macros only.

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