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function_exists

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

function_exists — Return true if the given function has been defined

Descrizione

function_exists(string $function): bool

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

Elenco dei parametri

function

The function name, as a string.

Valori restituiti

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

Nota:

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

Esempi

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";
}
?>

Note

Nota:

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).

Vedere anche: