How to use before_filter for auth

[eluser]gayathri[/eluser]
hi,

Thanks for your reply, i feel your suggestion is nice,

if(!$this->session->userdata('logged_in')) {
redirect('login', 'location');
}

this code, should i add for each and every function or only top of the controller, and if i want any expectional page, how to use that one? can you tell me please?