不使用子ID导航

i am just setting up the general template for my website and the little bit of php that i am doing is to just get the users id from page to page, in other words i want the user while logged in to go from page to page, without using the sub id in the header of user_id=3 for example, and then using the get function to get it and display their information, i want to be able to do it without that.

Here is my code but i keep getting the error

Notice: Undefined index: user_id in C:\xampp\htdocs\Arken\profile.php on line 7

LOGIN CODE (not all of it of course, just the bit for setting the sessions tuff)

// Create session var for their raw id
                $user_id = $row["user_id"];   
                $_SESSION['user_id'] = $user_id;
                // Create the idx session var
                $_SESSION['idx'] = base64_encode("g4p3h9xfn8sq03hs2234$id");
                // Create session var for their username
                $login_username = $row["login_username"];
                $_SESSION['login_username'] = $login_username;
                // Create session var for their password
                $login_userpass = $row["login_password"];
                $_SESSION['login_userpass'] = $login_userpass;

PHP for each page

    session_start();

$user_id = "";


if ($_GET['user_id']) {

     $user_id = $_GET['user_id'];

} else if (isset($_SESSION['user_id'])) {

     $user_id = $_SESSION['user_id'];

} else {

   include_once "index.php";
   exit();
}
include 'connect_to_mysql.php';

Thanks for your help

I am assuming line 7 is

if ($_GET['user_id']) {

Try making sure it's set before using it:

if (isset($_GET['user_id'])) {

This error is caused by the warning level E_NOTICE and this line:

if ($_GET['user_id'])

If the value for user_id is not set, this creates an error. If you only want to check whether or not the value is present, you should therefore use:

if (isset($_GET['user_id']))