count()：参数必须是一个数组或一个 object 实现 php 中的可计数错误

Question

I am creating an add-to-cart system in my website.

If there are no items in the cart, the variable $cart is set to NULL .

This results in the following error when I try to echo the number of items in the cart: count(): Parameter must be an array or an object that implements Countable .

Here's my php code:

<?php 
if ((isset($_SESSION['active_user_type']) && $_SESSION['active_user_type'] == "consumer") || !isset($_SESSION['active_user'])) {
?>
<div class="shopping_cart">
<div class="cart_title">
    <a href="view_cart.php">Shopping cart</a>
</div>

<?php
    $total = 0;
    if(isset($_SESSION['cart'])) {
        $cart = $_SESSION['cart'];
        for ($i=0; $i<count($cart); $i++) {
            $item_id = $cart[$i][0];
            $query = "SELECT * FROM items WHERE id=$item_id";
            $result = $db->query($query);
            if ($row = $result->fetch()) {
                $price = ($row['price']*$cart[$i][1]) + $row['shipping_price'];
            }
            $total += $price;
        }
    } else {
        $cart = NULL;
    }
?>
<div class="cart_details">
// the error seems to be from the line below:
    <?php echo count($cart); ?><br />
    <span class="border_cart"></span> Total: 
    <span class="price">
        <?php echo "BD " . number_format((float)$total,3,'.',''); ?>
    </span>
</div>
<div class="cart_icon">
    <a href="checkout.php" title="Checkout">
        <img src="images/shoppingcart.png" alt="" width="48" height="48" border="0" />
    </a>
</div>
</div>
<?php
}
?>

Answer 1

This is because you are counting on 'NULL', Try it like this:

.
.
.
else
{
    $cart = [];
}

Answer 2

When $cart == NULL (as it is assigned in your else clause) it is not count able since NULL does not have a Countable interface. As of PHP 7.2 , this results in the warning message you have seen.

But it seems you shouldn't try to output a cart when you don't have one, so you should just move that code inside your if block ie

$total = 0;
if(isset($_SESSION['cart']))
{
    $cart = $_SESSION['cart'];
    for ($i=0; $i<count($cart); $i++)
    {
        $item_id = $cart[$i][0];
        $query = "SELECT * FROM items WHERE id=$item_id";
        $result = $db->query($query);
        if ($row = $result->fetch())
        {
            $price = ($row['price']*$cart[$i][1]) + $row['shipping_price'];
        }
        $total += $price;
    }
?>
<div class="cart_details"> <?php echo count($cart);?> <br />
    <span class="border_cart"></span> Total: <span class="price"><?php echo "BD " . 
  number_format((float)$total,3,'.',''); ?></span> </div>
<div class="cart_icon"><a href="checkout.php" title="Checkout"><img src="images/shoppingcart.png" 
alt="" width="48" height="48" border="0" /></a></div>
 </div>
<?php
}
else
{
    $cart = NULL;
}
?>

Answer 3

It's because you're trying to count something that's not countable (how can you count the number of elements in null?). From the documentation:

7.2.0: count() will now yield a warning on invalid countable types passed to the array_or_countable parameter.

so prior to version 7.2.0 this warning wouldn't be emitted. In all versions, if obj in count(obj) isn't a valid array/countable object the function returns 1 , with the exception of count(null) which returns 0 .

---

You can either:

1. Cast it to an array
2. Explicitly set it to an empty array if it's empty
3. Put a check in place before echoing

1: <?php echo count((array)$cart);?>

2: else { $cart = []; } else { $cart = []; }

3: <?php ($cart == null)? '': echo count($cart);?> <?php ($cart == null)? '': echo count($cart);?>