function_exists

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

function_existsReturn 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).

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