How to make shortcut url

[eluser]Unknown[/eluser]
Hello,

I learnt about codeigniter and I found that there is a format of 'controller_name/function_name' in all the links of code igniter.
I need to make a dynamic shortcut url for a username such that I can access user's page by just typing for example http://www.example.com/user_name.

I think that I have to overwrite some class such that when code igniter can not find controller with name user_name then I must forward it to a controller that displays the user's profile which has user name equals to user_name specified in the url.

The problem is I don't know which files should I overwrite or perhaps any of you have a better solution in this? Thank you.

Teknokeras