function del()
{
    if ($_POST['lid'] == "") {
        return "-1";
    }
    $db = new DBClass();
    $sql = "SELECT uid FROM `app_lecture_info` WHERE lid = " . $_POST['lid'];
    $result = $db->query($sql);
    if ($result->num_rows <= 0) {
        return "-2";
    } else {
        $row = $result->fetch_assoc();
        $userObj = new UserClass();
        $permisson = $userObj->get_privilege($_SESSION['uid']);
        if ($_SESSION['uid'] != $row["uid"] && $permisson != '1') {
            return "-3";
        }
    }
    $lecture_inc = new LectureClass();
    $result = $lecture_inc->del_lecture($_POST['lid']);
    return $result;
}