url redirect

[eluser]Unknown[/eluser]
thanks your reply. Ye , i get the idea. but about 1 and 3 point . i can not understand clearly. My question's key is how to redirect back to the page before logining, it's url is Dynamic. such as domain/a/b or domain/b/c/d ...
i can not transfer the url of before page as a request querystring . even though using rawurlencode():

Code:

$preurl = $this->uri->uri_string();
             header("location:HTTP://".$_SERVER["HTTP_HOST"]."/login/index/".rawurlencode($preurl ));

ie prompt: 404 error no such page. why?
after check, location is such as: HTTP://".$_SERVER["HTTP_HOST"]."/login/index/a/b
why rawurlencode() no effect??