PHP autoloading namespace on xampp

I am trying to autoload php class under namespace on xampp. But for some reason it cannot find class under its absolute path.

here is my autoloader:

spl_autoload_register(function($className){
    require_once($_SERVER["DOCUMENT_ROOT"] .'/' . str_replace('\', '/', $className). '.php');
})

here is my class

namespace appadminmodulessmartForm;
class smartForm {
/* Class logic*/
}

This is my file system:

This i error i am getting:

Warning: require_once(C:/xampp/htdocs/app/admin/modules/smartForm/smartForm.php): Failed to open stream: No such file or directory in C:xampphtdocsphpsmartfromappsystemautoLoader.php on line 3

Answer

Looks like after 3 days i finally figure it out.

Instead of going trought absolute path you can choose relative path from autoloader file.

here is final include:

  include_once(__DIR__.'..\'.$className.'.php');