phpcms中如何判斷用戶是否登錄？

<?php         $userid= param::get_cookie(&#39;_userid&#39;); ?>

{if?$userid}??? ???????。。。這里寫已經登錄之后的代碼。。。 {else} ???????。。。這里寫已經登錄之后的代碼。。。 {/if}

defined('IN_phpcms')?or?exit('No?permission?resources.');  class?MY_index?extends?index?{  ????private?$times_db;  ????public?function?__construct()?{  ????????parent::__construct();  ????}  ????public?function?top_mini()?{  ????????$_username?=?param::get_cookie('_username');  ????????$_userid?=?param::get_cookie('_userid');  ????????$siteid?=?isset($_GET['siteid'])???intval($_GET['siteid'])?:?'';  ????????$jsoncallback=isset($_GET['jsoncallback'])???$_GET['jsoncallback']?:?'';  ????????//定義站點id常量  ????????if?(!defined('SITEID'))?{  ???????????define('SITEID',?$siteid);  ????????}  ????????if($_username){  ????????????$res["success"]=1;  ????????????$res["message"]='??'.L('hellow').';;;?'.get_nickname().'?歡迎回家?;'.L('member_center').';?|?;發布信息;?|?;'.L('logout').';';  ????????????$res["message"]?=?pc_base::load_config('system',?'charset')?==?'gbk'???iconv('utf-8',?'utf-8',?$res["message"])?:?$res["message"];  ????????????//get_nickname();//,  ?????????????  ????????????}  ????????else{  ????????????$res["success"]=0;  ????????????}  ?????????????  ????????if($jsoncallback){  ????????????echo?$jsoncallback?.?"({"items":[".json_encode($res)."]})";  ????????}else{  ????????????echo?json_encode($res);  ????????}  ????????//echo?json_encode($res);  ????}  ?  }  ?>