subdomain as class in codeigniter

<?php

// Thanks to Catfish on Stackoverflow - see http://goo.gl/5N17r

// /ci_starter/application/core/MY_controller.php

if (!defined('BASEPATH'))
    exit('No direct script access allowed');

class MY_Controller extends CI_Controller {

    protected $theme;
    protected $debug;
    protected $clean_output;
    public $subdomain = null;

    public function __construct() {
        parent::__construct();

    $url = $_SERVER['HTTP_HOST']; // Get the domain. EX: www.foo.example.com
    $host = explode('.', $url);
    $subdomain = $host[0];
    $this->subdomain = $subdomain;

        $this->layout->set_layout_dir('views/themes/' . $this->theme . '/layouts/');
        $layout_file = (!$this->mobiledetection->isMobile()) ? 'layout' : 'mobile_layout' ;
        $this->layout->set_layout($layout_file);
        if(!$this->clean_output){
            $this->layout->disable_clean_output();
        }
    }
}