... PHP 4 >= 4.0.5) array_search -- Searches the array for a given value and returns the corresponding key if successful . mixed array_search ( mixed needle, array haystack [, bool strict]) . Searches haystack for needle and returns the key if it is found in the array, FALSE otherwise. ... This function may return FALSE , but may also return a value evaluating to FALSE in a simple if statement. Please use the === operator for testing the return value of this function. See also in_array() . ...