在codeigniter中找不到类

In the below code i have used codeigniter code i have found a error class not found. Class 'Controller' not found in C:\wamp\www\todo1\application\controllers\login.php on line 3

<?php

class Login extends Controller {

    function index()
    {
        $data['main_content'] = 'login_form';
        $this->load->view('includes/template', $data);      
    }
?>

You need CI_Controller

class Login extends CI_Controller {

In codeigniter ( I think version 2.x.x ) you should use the following instead:

class Login extends CI_Controller {

    function index()
    {
        $data['main_content'] = 'login_form';
        $this->load->view('includes/template', $data);      
    }