Routing rules are defined in your application/config/routes.php file.

There is a one-to-one relationship between a URL string and its corresponding controller class/method. The segments in a URI normally follow this pattern:

example.com/class/function/id/

In some cases, you may want to remap this relationship so that a different class/method can be called instead of the one corresponding to the URL.

To learn how to implement routers on a real-world project, we will assume that we are creating an application for managing contact details. The following table shows the URLs that will be working with.

No.	URL	Route	Controller	Method
1	/	$route[‘default_controller’]	Contacts	index
2	/contacts	$route[‘contacts’]	Contacts	list
3	/contacts/add	$route[‘contacts/add’]	Contacts	add
4	/contacts/edit/id	$route[‘contacts/edit/(:num)’]	Contacts	edit
5	/contacts/update/id	$route[‘contacts/update/(:num)’]	Contacts	update
6	/contacts/delete/id	$route[‘contacts/delete/(:num)’]	welcome	delete

Create URLs for Applications

create routes for our project. Open application/config/routes.php

$route['default_controller'] 		= 'contacts';
$route['contacts'] 			= 'contacts/list';
$route['contacts/add'] 			= 'contacts/add';
$route['contacts/edit/(:num)']		= 'contacts/edit/$1';
$route['contacts/update/(:num)'] 	= 'contacts/update/$1';
$route['contacts/delete/(:num)'] 	= 'contacts/delete/$1';

$route['404_override'] 			= '';
$route['translate_uri_dashes'] 		= FALSE;

The following table shows the respective URLs obtained from the above-defined routes

No.	Route	URL
1	$route[‘default_controller’] = ‘contacts’;	http://localhost
2	$route[‘contacts’] = ‘contacts/list’;	http://localhost/contacts
3	$route[‘contacts/add’] = ‘contacts/add’;	http://localhost/contacts/add
4	$route[‘contacts/edit/(:num)’] = ‘contacts/edit/$1’;	http://localhost/contacts/edit/1
5	$route[‘contacts/update/(:num)’] = ‘contacts/update/$1’;	http://localhost/contacts/update/1
6	$route[‘contacts/delete/(:num)’] = ‘contacts/delete/$1’;	http://localhost/contacts/delete/1