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function_exists

PHP function Edit on GitHub ✎

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

Return true if the given function has been defined

Description

function_exists(string $function): bool

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

Parameters

function: The function name, as a string.

Return Values

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

Note

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

Examples

function_exists() example

php

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

Notes