php - Display error message from Admin_Controller -

i had create core/admin_controller.php , created page controller when run page controller there error displaying "fatal error: class 'admin_controller' not found in d:\xampp\htdocs\myproject\application\controllers\admin\page.php on line 4"

class admin_controller extends my_controller  {      function __construct()      {                     parent::__construct();                }    }

page controller

defined('basepath') or exit('no direct script access allowed');    class page extends admin_controller {    	public function __construct()  	{  		parent::__construct();  		$this->load->model('admin_m');  		$this->load->model('page_m');  	}    	public function index(){  		$data['title'] = 'press release';          $data['page'] = $this->page_m->show_list();          $this->load->view(theme_dir_admin.'common/admin_header');          $this->load->view(theme_dir_admin.'page/list', $data);          $this->load->view(theme_dir_admin.'common/admin_footer');  	}  }	

need update file?

core/admin_controller.php

class admin_controller extends ci_controller {     function __construct()     {          parent::__construct();     } } 

and

config/config.php

$config['subclass_prefix'] = 'admin_';