注意:未初始化的字符串偏移量:2

function forums($name, $id){
$forums = "";
$sql = mysql_query("SELECT * FROM ".prefix."FORUM WHERE FORUM_ID = '$id' ") or die(mysql_error());
if(mysql_num_rows($sql)>0){
    $rs = mysql_fetch_array($sql);
    $forums = Array(
        $rs[CAT_ID], $rs[F_STATUS], $rs[F_SUBJECT]
        );
}
if ($name == "CAT_ID"){$nom = 0;}
if ($name == "STATUS"){$nom = 1;}
if ($name == "SUBJECT"){$nom = 2;}

return($forums[$nom]);
mysql_free_result($sql);
}

我收到此错误：

注意：未初始化的字符串偏移量：2 在 C：''xampp''htdocs''cp_inc''function.php 第 1589 行