来请问一个有关问题

<br>
<!--?php<br /-->
define('ACCESE',1);<br>
require('../init.php');<br>
<br>
$_GET['gid'] = (int)$_GET['gid'];<br>
$_GET['num'] = (int)$_GET['num'];<br>
<br>
$goods = new goodsModel();<br>
$goods->db();<br>
$cart = cart::getCart();<br>
<br>
switch($_GET['act']) {<br>
        //添加商品<br>
        case 'buy':{<br>
                $result = $goods->select_goods("g_id = $_GET[gid] and g_sale=1 and g_del=0");<br>
                $g = $goods->db->fetch_array($result);<br>
                //有此商品<br>
                if(!empty($g)) { //判断商品是否存在<br>
                        if($g['g_no'] < $_GET['num']) { //判断库存<br>
                                $type = 'error';<br>
                                $msg = '放到购物车添加失败（可能是库存不足或者管理员私吞了）';<br>
                                include(ROOT.'view/home/tip.html');<br>
                                exit;<br>
                        }<br>
                        //商品存在<br>
                        $cart->addItem("$g[g_id]","$g[g_name]","$g[g_price]","$_GET[num]");   //----------------------此行报错<br>
                } else {<br>
                        $type = 'error';<br>
                        $msg = '放到购物车添加失败（可能是下架、删除或者管理员私吞了）';<br>
                        include(ROOT.'view/home/tip.html');<br>
                        exit;<br>
                }<br>
                break;<br>
        }<br>
<br>
}<br>
<br>
$title = '购物车 - 商城系统';<br>
$path = '购物车';<br>
include(ROOT.'view/home/cart.html');