php 实现购物车

<?php 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0             return 0;         }           $sum = 0;         $data = $_SESSION['cart'];         foreach ($data as $item) {             $sum += $item['num'];         }         return $sum;     }       /*     购物车中商品的总金额     */     public function getPrice() {         //数量为0，价钱为0         if ($this->getCnt() == 0) {             return 0;         }         $price = 0.00;         $data = $_SESSION['cart'];         foreach ($data as $item) {             $price += $item['num'] * $item['price'];         }         return sprintf("%01.2f", $price);     }       /*     清空购物车     */     public function clear() {         $_SESSION['cart'] = array();     } }