function_exists

(PHP 4, PHP 5, PHP 7)

function_exists — Return TRUE if the given function has been defined

설명

bool function_exists ( string $function_name )

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

인수

function_name: The function name, as a string.

반환값

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.

예제

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";
}
?>

주의

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).

참고

method_exists() - 클래스 메쏘드가 존재하는지 확인
is_callable() - 변수 내용을 함수처럼 호출할 수 있는지 확인
get_defined_functions() - Returns an array of all defined functions
class_exists() - 클래스가 정의되었는지 확인
extension_loaded() - Find out whether an extension is loaded