function_exists
(PHP 3 >= 3.0.7, PHP 4, PHP 5)
function_exists -- Return
TRUE if the given function has been defined
Description
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.
Examples
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";
}
?>
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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).
