URI routing in Codeigniter

The routes.php file lets you remap URI requests to specific controller functions. For example, you may
have a controller named site with a function named index . The URI for this controller/function
combination might be :

http://www.example.com/site/index

Furthermore, if your site controller had a pages function that accepted a numeric ID for database
lookup, the URI might look like this:

http://www.example.com/site/pages/4

In some cases, you might want to remap one or more of these default routes. For example, the second
example might be better displayed as this:

http://www.example.com/about_us/

In that case, your routes.php file would contain a rule like this:

$route[‘about_us’] = “site/pages/4”;

For right now, though, this kind of manipulation falls under “ advanced usage, ” so don ’ t worry too much
about it. However, please do note that this kind of thing is possible. Also, be aware that two “ reserved
routes ” exist: default_controller and scaffolding_trigger.

$route[‘default_controller’] = “welcome”;

The default_controller route tells CodeIgniter which controller should be loaded if no controller is
identified. For simplicity ’ s sake, keep this setting at welcome, because you ’ re going to create a welcome
controller for the project associated with this book.

To know more about URI routing Please visit the below link
http://codeigniter.com/user_guide/general/routing.html