Route / cannot access function in my controller

[eluser]leaflashdev[/eluser]
Hello

I set up a simple project
I created a controller called portfolio.php in the /controllers/ folder
inside the routes.php class I wrote this line
$route['default_controller'] = "portfolio";
So now if I go on http://localhost:8888/portfolio/ it access my function called index
but If I do http://localhost:8888/portfolio/index or http://localhost:8888/portfolio/dosomething
it seems that the function is not found
Don't really know why

I tried to replace $route['default_controller'] = "portfolio/dosomething";
and when I go back to http://localhost:8888/portfolio I have my echo test
function dosomething(){
echo 'test';
}

Any ideas ?

Thanks !