Facebook API does not return userid

Facebook API does not return userid

require '../src/facebook.php';
// Create our Application instance (replace this with your appId and secret).
$config = array();
$config['appId'] = '109181812948600';
$config['secret'] = 'edflmlkmlkmlkmlkmlk7079e9d5884';
$config['fileUpload'] = false; // optional
$facebook = new Facebook($config);
$uid = $facebook->getUser();
echo $uid;
Returning userid as 0. i just want to access my photos which i uploaded in
the FB.