php session 购物车类

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'] 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;
		}
		$price = 0.00;
		foreach ($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();
	}
}