Multi site with subfolders by subdomain

Hi,

I'm trying to make a multi site with subfolder by subdomain, baut i'm having problems with default controller:

The directory escructure is:
application
  controllers
    mobile
      Home.php
    api
      Home.php
    desktop
      Home.php

And the code in router (that works in codeigniter 2.x) is the following:

PHP Code:

$hostParts = explode('.', $_SERVER['HTTP_HOST']);
$subdomain = $hostParts[0];
switch ($subdomain) {
    case 'm':
        $controllersFolder = 'mobile';
        $defaultController = 'home';
        break;
    case 'api':
        $controllersFolder = 'api';
        $defaultController = 'home';
        break;
    default:
        $controllersFolder = 'desktop';
        $defaultController = 'home';
        break;
}

// defaults
$route['default_controller'] = $controllersFolder.'/'.$defaultController; 


I read something like that this works in codeigniter 2.x because is a bug, if this is the reason, what is the correct way to make it?

Greetings.