Calling a Controller function in another Controller in CodeIgniter

I have a controller "user" in my codeigniter application. This controller has a function called logged_user_only():

public function logged_user_only()
    {
        $is_logged = $this -> is_logged();
        if( $is_logged === FALSE)
        {
            redirect('user/login_form');
        }
    }

As this function calls another function called is_logged(), which just checks if the session is set, if yes it returns true, else returns false.

Now if i place this function in the begining of any function within same controller, it will check if the user is not logged, it will redirect to login_form otherwise continue. This works fine. For example,

public function show_home()
    {
        $this -> logged_user_only();
        $this->load->view('show_home_view');
    }

Now I would like to call this logged_user_only() function in a function of another controller to check if the user is logged in or not?

PS. If this can not be done, or is not recommended, where should i place this function to access in multiple controllers? Thanks.