HOME |
(PHP 4, PHP 5)
function_exists — Return TRUE
if the given function has been defined
$function_name
)
Checks the list of defined functions, both built-in (internal) and
user-defined, for function_name
.
function_name
The function name, as a string.
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.
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:
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).