Can't get variables from SESSION - php

Question

I'm having a problem with my school project. I've asked both my teacher and classmates for help but none of them doesn't know what to do.
I've made a browser based game, and obviously it needs to have users. And this is where the problem is.
When i log in and proceed to the authenticate page, it extracts info from POST just fine, but when i insert the info into SESSION in authenticate and then go to the homepage index, it refuses to get the SESSION information and i just get an error.
NOTE, design2.php doesnt have anything to do with the log in process.
Here's the code:
Login.php
<?php
include_once'design2.php';
?>
<div id="center">
<form method="POST" action="authenticate.php">
User Name <input id="input" type="text" name="player" size="21">
Password <input id="input" type="password" name="password" size="21">
<br>
<input type="submit" value="Login" name="submit">
<br><br>Not Registered? <a id='underlinelink' href='register.php'>Register</a>
Authenticate.php
<?php
include_once 'connect.php';
?>
<div id="center">
<?php
if (isset($_POST['submit']))
{
$player=$_POST['player'];
$password=$_POST['password'];
$player=strip_tags($player);
$password=strip_tags($password);
$password=md5($password);
$query = "select name, password from players where name='$player' and password='$password'";
$result = mysql_query($query) or die("Could not query players");
$result2 = mysql_fetch_array($result);
if ($result2)
{
$_SESSION['player'] = $player;
echo "<big>Logged in successfully<br>";
echo "<A id='underlinelink' href='index.php'>Continue</a></big>";
}
else
{
echo "<big>Wrong username or password.<A id='underlinelink' href='login.php'>Try Again</a></big>";
}
}
?>
</div>
Design.php (This is on every single webpage on my site)
<?php
include_once 'connect.php';
?>
<link href="stilark.css" rel="stylesheet" type="css" />
<?php
session_start();
if(isset($_SESSION['player']))
$player = $_SESSION['player'];
else
echo "could not logg in, <a href='login.php'>Go back</a>";
exit;
$playerinfo="SELECT * from players where name='$player'";
$playerinfo2=mysql_query($playerinfo) or die("could not get player stats!");
$playerinfo3=mysql_fetch_array($playerinfo2);
?>
Please help, i really need to get this done before its due.

Answer 1

You need to create or resume the session before you write into it. So in your Authenticate.php where you do $_SESSION['player'] = $player;, create a session first exactly as you do it in your other files. Something like that
Authenticate.php
<?php
session_start();
include_once 'connect.php';
?>
<div id="center">
<?php
// Rest of your code
// ...
if ($result2)
{
$_SESSION['player'] = $player;
// and so on...
Also, as #DamienLegros noted in his answer, you should always have the session_start() statement as early as possible in your code, i.e. as one of the first statements, so you make sure no output has been made before it's started. Otherwise you'll start getting errors stating that headers has already been sent.

Answer 2

Your session_start() must be BEFORE any output
<?php
session_start();
include_once 'connect.php';
?>
<link href="stilark.css" rel="stylesheet" type="css" />

Answer 3

<?php
session_start();
include_once 'connect.php';
?>
<div id="center">
<?php
if (isset($_POST['submit']))
...
...
...
note: add session_start(); at the top of your Authenticate.php page