function_exists

(PHP 4, PHP 5, PHP 7, PHP 8)

function_exists — Return true if the given function has been defined

Опис

function_exists(string $function): bool

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

Параметри

function: The function name, as a string.

Значення, що повертаються

Returns true if function exists and is a function, false otherwise.

Зауваження:
This function will return false for constructs, such as include_once and echo.

Приклади

Приклад #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";
}
?>

Примітки

Зауваження:
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).

Прогляньте також

method_exists() - Checks if the class method exists
is_callable() - Verify that a value can be called as a function from the current scope
get_defined_functions() - Returns an array of all defined functions
class_exists() - Checks if the class has been defined
extension_loaded() - Визначає - чи розширення завантажено