I've been searching for hours for the solution to this problem but can't find one that works for me. When i click "Logout" on my site the user information is still visible and the logout button is still displayed. Here is the code:

require 'facebook-php-sdk/src/facebook.php';

$facebook = new Facebook(array(
  'appId'  => 'xxxx',
  'secret' => 'xxxx',
));

// Get User ID
$user = $facebook->getUser();
var_dump($user);
if ($user) {
  try {
    // Proceed knowing you have a logged in user who's authenticated.
    $user_profile = $facebook->api('/me');
  } catch (FacebookApiException $e) {
    error_log($e);
    $user = null;
  }
}

// Login or logout url will be needed depending on current user state.

if ($_GET['logout'] == "yes") {
setcookie('fbs_'.$facebook->getAppId(), '', time()-100, '/', 'http://gno.....ment/index.php');
session_destroy();
header("Location: ".$_SERVER['PHP_SELF']."");
}

if ($user_profile) {
  $logoutUrl = $facebook->getLogoutUrl;
} else {
  $loginUrl = $facebook->getLoginUrl(array('scope' => 'email,publish_stream,user_status',
  'canvas' => 1,
  'fbconnect' => 0,
  'redirect_uri' => 'http://gno.....ment/index.php'));
}

..... .....

<?php if ($user): ?>
<h3>You</h3>
<img src="https://graph.facebook.com/<?php echo $user; ?>/picture">

<h3>Your User Object (/me)</h3>
<pre><?php print_r($user_profile); ?></pre>
<?php else: ?>
<strong><em>You are not Connected.</em></strong>
<?php endif ?>

<?php if ($user): ?>
<a href="<?php echo $logoutUrl; ?>">Logout of FB</a>
<?php else: ?>
<div>
Login using OAuth 2.0 handled by the PHP SDK:
<a href="<?php echo $loginUrl; ?>">Login with Facebook</a>
</div>
<?php endif ?>

It seems that if ($_GET['logout'] == "yes") might be the answer for me but i can't get it working. I don't know where logout is gotten from or where it is defined?

This seems to be a common issue but i can't figure it out. I'd really appreciate some help.