PHP Reference

Description

bool function_exists ( string function_name)

Checks the list of defined functions, both built-in (internal) and user-defined, for function_name. Returns TRUE on success or FALSE on failure.


<?php

if (function_exists('imap_open')) {

    echo "IMAP functions are available.<br />\n";

} else {

    echo "IMAP functions are not available.<br />\n";

}

?>

Note that 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). Also note that function_exists() will return FALSE for constructs, such as include_once() and echo().