call form_open() with action outside webroot

[eluser]Unknown[/eluser]
I have my apps outside webroot.

config:
$config['base_url'] = "http://localhost/cart/";

index:
$system_path = '/wamp/CodeIgniter/system';
$application_folder = '/wamp/CodeIgniter/application/cart';

When i run form_open('shop/add')

i get this url: http://localhost/cart/shop/add
and the 404 error.

How to find and run ok the controller 'shop' and the function 'add' if they are outside of webroot using form_open()?

Can you help me please.

[eluser]Unknown[/eluser]
SOLVED: I assigned index.php to index_page in config, php.