function_exists Return TRUE if the given function has been defined php函数


function_exists

(PHP 4, PHP 5)

function_existsReturn TRUE if the given function has been defined

说明

bool function_exists ( string $function_name )

Checks the list of defined functions, both built-in (internal) and user-defined, for function_name.

参数

function_name

The function name, as a string.

返回值

Returns TRUE if function_name exists and is a function, FALSE otherwise.

Note:

This function will return FALSE for constructs, such as include_once() and echo().

范例

Example #1 function_exists() example

<?php
if (function_exists('imap_open')) {
    echo 
"IMAP functions are available.<br /> ";
} else {
    echo 
"IMAP functions are not available.<br /> ";
}
?>

注释

Note:

A function name may exist even if the function itself is unusable due to configuration or compiling options (with the image functions being an example).

参见



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