Session not being saved after logging in - php

Question

Another attempt at designing a user membership. Got to log in successfully, finds the data in the database. But in my index file, after logging in, it should check if I'm logged in and display links to my account instead of register and login. Here's the code:
<?php
session_start(); // Must start session first thing
// See if they are a logged in member by checking Session data
$toplinks = "";
if (isset($_SESSION['id'])) {
// Put stored session variables into local php variable
$userid = $_SESSION['id'];
$username = $_SESSION['username'];
$toplinks = '' . $username . ' •
Account •
Log Out';
} else {
$toplinks = 'Register • Login';
}
?>
And here is the login form code, where I think the problem is because it's not storing my session id:
<?php
if ($_POST['email']) {
//Connect to the database through our include
include_once "connect_to_mysql.php";
$email = stripslashes($_POST['email']);
$email = strip_tags($email);
$email = mysql_real_escape_string($email);
$password = preg_replace("[^A-Za-z0-9]", "", $_POST['password']);
// filter everything but numbers and letters
$password = md5($password);
// Make query and then register all database data that -
// cannot be changed by member into SESSION variables.
// Data that you want member to be able to change -
// should never be set into a SESSION variable.
$sql = mysql_query("SELECT * FROM users WHERE email='$email' AND password=
'$password'AND emailactivated='1'");
$login_check = mysql_num_rows($sql);
if($login_check > 0){
while($row = mysql_fetch_assoc($sql)){
// Get member ID into a session variable
$userid = $row["id"];
$_SESSION['id'] = $userid;
// Get member username into a session variable
$username = $row["username"];
$_SESSION['username'] = $username;
// Update last_log_date field for this member now
mysql_query("UPDATE users SET lastlogin=now() WHERE id='$userid'");
// Print success message here if all went well then exit the script
header("location: member_profile.php?id=$userid");
exit();
} // close while
} else {
// Print login failure message to the user and link them back to your login page
print '<br /><br /><font color="#FF0000">No match in our records, try again
</font> <br/>
<br />Click here to go back to the login page.';
exit();
}
}// close if post
?>
Once again I'm following someone's tutorial and trying to implement it to my website and this would be perfect if it worked. Please advice why the $toplinks aren't being set after logging in.

Answer 1

I think the problem is, that you have to include the session_start() in every file where you want to use your session. Otherwise its working in the file like a normal array but not global. In your form i can't see that you start your session.
Edit: You need this only if you have 2 files. When you have only one file and include the other page its working when you include in once on top.

Answer 2

If you want to log out, then you should create a logout file, and include
session_destroy();
probably add also a href to get redirection link by doing something like:
header('location:index.php'); // will return you to index as soon as you logout.