Skip to execute construct method when certain method called

Sometime we don't need to execute any method / code inside constructor/destructor.
example for codeigniter

class Student
{

public function __construct ()

{

        // we want to skip 2 methods(login and logout) in this 'student' class.

$exception_uris = array(

'student/login', 

'student/logout'

);

//  check called class and method from URL.If  called method are not those login/logout execute code

 
if (in_array(uri_string(), $exception_uris) == FALSE)
   {

 
       if ($this->student_m->loggedin() == FALSE)
      {

redirect('student/login');

}

}    

}

}