main core url file ???

[eluser]aman_tuladhar[/eluser]
File that you are looking for is system/core/Router.php

you can try code like this:

Code:

$router =& load_class('Router');
$router->fetch_class();     // name of controller
$router->fetch_method();    // name of function
$router->fetch_directory(); // name of current directory
...