problem with session in template

I created MY_Controller in application/core/ and this is the code:

PHP Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class MY_Controller extends CI_Controller {

        public function __construct() {
                parent::__construct();
        }

        public function index() {
                $session_data = $this->session->userdata('logged_in');
                $data['username'] = $session_data['login'];
                $this->smarty->assign('user_log', $session_data);
        }

} 


In the all other controller I edit in this way:

PHP Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class NameClass extends MY_Controller { 


But when I try to access in the page I found this error:

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined index: user_log

Filename: compiled/c3a9b50f1375d1dde5af34b18cf8ecc0df629901.file.rightSide.tpl.php

Line Number: 33

Backtrace:

Code:

A PHP Error was encountered

Severity: Notice

Message: Trying to get property of non-object

Filename: compiled/c3a9b50f1375d1dde5af34b18cf8ecc0df629901.file.rightSide.tpl.php

Line Number: 33

How should I do?

Sorry but it is the first time that I attempt to well with CI


EDIT: If I move 

Code:

$session_data = $this->session->userdata('logged_in');
               $data['username'] = $session_data['login'];
               $this->smarty->assign('user_log', $session_data);

In the __construct() session data makes them see me but this is the error:

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined index: username

Filename: compiled/c3a9b50f1375d1dde5af34b18cf8ecc0df629901.file.rightSide.tpl.php

Line Number: 35