php - 无法增加/减少 php 中的重载对象或字符串偏移量

Question

我正在尝试制作一个简单的 php 购物车。我不知道如何自己制作一个，所以我尝试搜索，发现对于像我这样的初学者来说，这是最容易理解的:http://jameshamilton.eu/content/simple-php-shopping-cart-tutorial唯一的问题是我在这行代码中收到标题中提到的错误:

$_SESSION['cart'][$product_id]++;

完整代码如下:

        $product_id = $_GET['id'];   //the product id from the URL 
        $action     = $_GET['action']; //the action from the URL 

        //if there is an product_id and that product_id doesn't exist display an error message
        if($product_id && !productExists($product_id)) {
            die("Error. Product Doesn't Exist");
        }

        switch($action) {   

            case "add":
                $_SESSION['cart'][$product_id]++; //add one to the quantity of the product with id $product_id 
            break;

            case "remove":
                $_SESSION['cart'][$product_id]--; //remove one from the quantity of the product with id $product_id 
                if($_SESSION['cart'][$product_id] == 0) unset($_SESSION['cart'][$product_id]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. 
            break;

            case "empty":
                unset($_SESSION['cart']); //unset the whole cart, i.e. empty the cart. 
            break;

        }

    ?>

我还在 php 设置上启用了注册全局变量。我该如何解决这个问题？

Answer 1

改用 +1:$_SESSION['cart'][$product_id] = $_SESSION['cart'][$product_id] + 1; 应该可以解决问题。