How to send id to controller in codeigniter -

i'm using below code site, displayed me

404: page not found.

routes

$route['class_name/function_name/(:num)'] = 'class_name/function_name/$1'; 

controller.

 public function function_name($id)     {         print_r($id); exit;     } 

use uri extract id url: following link in docs : http://www.codeigniter.com/userguide2/libraries/uri.html

example- how url using uri_string() codeigniter?