unexpected array_diff output

Hello there ! I am trying to fill and then compare two arrays: one filled by a foreach construct, and the second by a while construct. I check both with a print_r to be sure that both are correctly filled (which seems to be the case). But then, when I try to compare them with a array_diff , the result is incoherent (at least to me...). I have tried several variant, but I don't understand what's wrong. Sure you guys can tell me where is my mistake. Here is the code: <? // creates first array (from a _POST[''] ) foreach ($_POST['input_auteur'] AS $aut_ligne) { $part_ligne = explode(",",$aut_ligne); $arr1[] = (string) $part_ligne['2']; } echo "Array from POST :"; print_r ($arr1); // creates second array (from SQL query) $sqlListAut = 'SELECT aut_id FROM mr_ecrit WHERE doc_id = ' . $_GET['docu']; $resultListAut = mysql_query($sqlListAut); while ($recListAut = mysql_fetch_array($resultListAut)) { $arr2[] = (string) $recListAut['aut_id']; } echo "Array from SQL:<BR>"; print_r ($arr2); // comparing both arrays to detect if there is elements in the first array which are not present in the second array $result = array_diff($arr1, $arr2); echo "array_diff results :"; print_r($result); ?> Here is a typical output: __________________________________________ Array from POST: Array ( [0] => 2 [1] => 3 [2] => 4 ) Array from SQL : Array ( [0] => 3 [1] => 4 ) ****** array_diff results : Array ( [0] => 2 [1] => 3 [2] => 4 ) __________________________________________ As you can see, the array_diff seems to always return all elements of the first array. Thanks for your help. Best regards, Fred Noyer