PHP编写一个购物车的类

<?php//购物车的类class Cart{public function Cart() {if(!isset($_SESSION['cart'])){$_SESSION['cart'] = array();}}/*添加商品param int    $id    商品主键  string $name  商品名称  float  $price 商品价格  int    $num   购物数量*/public  function addItem($id,$name,$price,$num,$img) {//如果该商品已存在则直接加其数量if (isset($_SESSION['cart'][$id])) {$this->incNum($id,$num);return;}$item = array();$item['id'] = $id;$item['name'] = $name;$item['price'] = $price;$item['num'] = $num;$item['img'] = $img;$_SESSION['cart'][$id] = $item;}/*修改购物车中的商品数量int $id 商品主键int $num 某商品修改后的数量，即直接把某商品的数量改为$num*/public function modNum($id,$num=1) {if (!isset($_SESSION['cart'][$id])) {return false;}$_SESSION['cart'][$id]['num'] = $num;}/*商品数量+1*/public function incNum($id,$num=1) {if (isset($_SESSION['cart'][$id])) {$_SESSION['cart'][$id]['num'] += $num;}}/*商品数量-1*/public function decNum($id,$num=1) {if (isset($_SESSION['cart'][$id])) {$_SESSION['cart'][$id]['num'] -= $num;}//如果减少后，数量为0，则把这个商品删掉if ($_SESSION['cart'][$id]['num'] <1) {$this->delItem($id);}}/*删除商品*/public function delItem($id) {unset($_SESSION['cart'][$id]);}/*获取单个商品*/public function getItem($id) {return $_SESSION['cart'][$id];}/*查询购物车中商品的种类*/public function getCnt() {return count($_SESSION['cart']);}/*查询购物车中商品的个数*/public function getNum(){if ($this->getCnt() == 0) {//种数为0，个数也为0return 0;}$sum = 0;$data = $_SESSION['cart'];foreach ($data as $item) {$sum += $item['num'];}return $sum;}/*购物车中商品的总金额*/public function getPrice() {//数量为0，价钱为0if ($this->getCnt() == 0) {return 0;}$price = 0.00;foreach ($this->items as $item) {$price += $item['num'] * $item['price'];}return sprintf("%01.2f", $price);}/*清空购物车*/public function clear() {$_SESSION['cart'] = array();}}