public function query($res, $pass_no = 1) {
    $q1 = mysqli_query($res, $this->db_link);
    if (!$q1) {
        $this->sql_error();
        if ($pass_no == 1) {
            if ($this->output_error == 1) {
                echo 'Attempting to reconnect to MySQL...' . "n";
            }
            $this->db_close();
            $this->db_connect();
            $this->query($res, 2);
        } else {
            if ($this->output_error == 1) {
                echo 'Reconnection failed; please check your MySQL server settings!' . "n";
            }
        }
    } else {
        return $q1;
    }
}

global  $db ;

$username = mysqli_real_escape_string($_POST['username_login']);

      $q ="select * from ".DB_PREFIX."admins where username='".$username."' ".
        "and password='".md5( $_POST['password_login'])."'";
   // echo $q;
    $res =$db->query($q);
    if($db->num_rows($res)==1)
    {

        return true ;
    }

return false ;