php - using static variable in different controller -

i'm making application i'm saving user information in user controller of code igniter application inside static variable, want access static variable in other controller, how can approach that? code here

<?php       class user extends ci_controller{           public static $user_data = array();           public __construct()           {                parent::__construct();                self::$user_data = array('value'); // values model           }      }      // can user static variable view in controller      class friends extends ci_controller{           public __construct()           {                parent::__construct();                if(user::$user_data->isfriends)                {                      redirect('person/'.user::$user_data->id);                }           }      }      // how can access functionality in codeigniter? gives error undefined class user not found 

static::$user_data = array('value') 

shouldn't self::... in user class?