Hooks v CI

Zdravim, v CI bych chtěl použít autentizaci, která bude volána pomocí hooks, ale není mi jasný rozdíl mezi těmito 3: pre_controller Called immediately prior to any of your controllers being called. All base classes, routing, and security checks have been done. post_controller_constructor Called immediately after your controller is instantiated, but prior to any method calls happening. post_controller Called immediately after your controller is fully executed. respektive ten post_controller_constructor mi není moc jasný. Můžete mi poradit jak ten funguje? Díky http://codeigniter.com/user_guide/general/hooks.html