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Return TRUE if the given function has been defined
Function handling Functions
PHP Manual

function_exists

(PHP 4, PHP 5)

function_existsReturn TRUE if the given function has been defined

Description

bool function_exists ( string $function_name )

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

Parameters

function_name

The function name, as a string.

Return Values

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.

Examples

Example #1 function_exists() example

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

Notes

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).

See Also


Function handling Functions
PHP Manual