[PHP] problem z array_diff_key() Opcje

[kufalo]

index.php

[PHP] pobierz, plaintext 
<?
 $a=$b=array();
 $c=array_diff_key($a,$b);
?>
[PHP] pobierz, plaintext 

(IMG:http://forum.php.pl/uwaga.gif)
poprawiam
---
nospor

Fatal error: Call to undefined function array_diff_key() in index.php on line 3

Dodam ze mam:

Apache/2.0.55 (Win32) php/5.0.5