最新版本的localhost中的变量未定义错误（vertrigo_230）

Question

下面提到的PHP代码在vertrigo_222（以及livehost）上也很完美。
现在我正在尝试将本地主机升级到vertrigo_230。
我面临以下未定义的变量错误或警告： 这是代码（提到第30行）：

<?php
ob_start();
session_start();
include_once("PHP_Code/db_connection.php");
if(isset($_REQUEST['data']))
    $data = $_REQUEST['data'];

//Fetch All Important Information from Database in Variables
if($_SESSION['id'] && $_SESSION['pw'])  //Login Must for This Informatiion
{
    if(isset($_REQUEST['city_id']))
    {
        if($_REQUEST['city_id'])
        {
            $city_id = $_REQUEST['city_id'];
        }
        else
        {
            $query = "SELECT * FROM cities WHERE user_id = '$_SESSION[id]'";
            $c = mysql_query($query) or die(mysql_error()." in query $query");
            $city = mysql_fetch_array($c);
            $city_id = $city['city_id'];
        }
        //Setting Current/Opened City in Session
        $_SESSION['city_id'] = $city_id;
    }
}

//Secure Page
if($data == "")                   //Line # 30
    $data = "loginPage";

请给我一些解决方案。

Answer 1

将$data定义为全局变量，您必须使用mysqli insted，因为mysql已正式弃用

  ob_start();
session_start();
include_once("PHP_Code/db_connection.php");
$data = '';
//your code