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function_exists

Return TRUE if the given function has been defined (PHP 4, PHP 5)
bool function_exists ( string function_name )

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

Parameters

function_name

The function name, as a string.

Return Values

Returns TRUE if function_name exists and is a function, FALSE otherwise.

Note:

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

Examples

Example 761. 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";
}
?>


Notes

Note:

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).