1. 用于后台登录验证 

   post_controller_constructor

<?php

class Auth {
   
   private $CI;
   private $loginUri = 'welcome/login';
   private $loginAuth = FALSE;
   private $sessId = null;
   
   public function __construct(){
      $this->CI = &get_instance();
      $this->CI->load->helper('url');
      $this->initSession();
      $this->setLoginAuth();
   }
   
   
   public function initSession(){
      if(session_status()===1){
         session_name(SESS_NAME);
         if($this->sessId!==null){
            session_id($this->sessId);
         }
         $lifeTime = 24 * 3600; 
         session_set_cookie_params($lifeTime); 
         session_start();
      }
   }
   
   public function setLoginAuth(){
      if(!empty($_SESSION['admin_user_id'])){
         $this->loginAuth = TRUE;
      }
   }
   
   public function chkLoginAuth(){
      if(!$this->loginAuth && !in_array(uri_string(),array('login', 'login/ajaxsub'))){
         redirect($this->loginUri);
      }
      return TRUE;
   }
}