json_decode解析的问题

$jsoninfo = json_decode($result);  
$errcode = $jsoninfo -> errcode;  //正常
$errmsg = $jsoninfo -> errmsg;    //正常
$card = $jsoninfo -> card;
$cardid = $card -> card_id;          //null

$cardid应该怎么取啊，取出来为空，上面的操作不行，求助各位！

这样写是正确的，谢谢大家！

$jsoninfo = json_decode($result);

$errcode = $jsoninfo -> errcode; //正常
$errmsg = $jsoninfo -> errmsg; //正常
$card = $jsoninfo -> card;
$cardid = $card -> card_id; //null