Check method/function exist with Controller

Hi guys,

can anyone please help, how can i check if method/funcion exist within class/controller? say:

PHP Code:

class User extends CI_Controller {
    public function __construct() {
      parent::__construct();
    }

    public function login() {
       ...
    }
} 


the idea is, i want to check function "login()" if exist and execute.

hope someone could help.

Thanks in advanced