Question

这让我很难过。 print_r显示正确的数组索引和值，但foreach构造检索错误的值，甚至更改最后一个索引的值，即使我没有通过引用检索值（不使用＆符号）。

<?php

require './includes/dbal.php';
require './includes/user.php';
require './includes/book.php';

session_start();

$title='My Shopping Cart';
include './template/header.php';

if(!isset($_SESSION['user']))
{
    die('You are not logged in.');
}

if(!isset($_SESSION['cart']))
{
    $_SESSION['cart'] = array();
}

if(isset($_POST['submit']) && strcmp($_GET['mode'], 'add') == 0)
{
    if(filter_var($_POST['qty'], FILTER_VALIDATE_INT) == FALSE)
    {
        echo '<div style="color: red;">Invalid quantity specified. Please go back and use a valid quantity.</div>';
    }
    else
    {
        $_SESSION['cart'][$_POST['book_id']] = $_POST['qty'];
    }
}

else if(isset($_POST['update']) && strcmp($_GET['mode'], 'update') == 0)
{
    foreach($_SESSION['cart'] as $key => &$value)
    {
        if((int) $_POST["qty_$key"] === 0)
        {
            unset($_SESSION['cart']["$key"]);
        }
        else
        {
            $value = $_POST["qty_$key"];
        }
    }
}

echo '<h3>Your shopping cart</h3>';

$db = new DBal();
$total=0;
echo '<div id="cart-items"><ul><form action="./cart.php?mode=update" method="post">';

// echo 'Original array: '; print_r($_SESSION['cart']);
foreach($_SESSION['cart'] as $key => $value)
{
    // echo '<br />$key => $value for this iteration: ' . "$key => $value<br />";
    // print_r($_SESSION['cart']);
    $b = new Book($key, $db);
    $book = $b->get_book_details();
    $total += $value * $book['book_nprice']
?>
<li>
    <div><img src="./images/books/thumbs/book-<?php echo $book['book_id']; ?>.jpg" title="<?php echo $book['book_name']; ?>" /></div>
    <span class="cart-price">Amount: Rs. <?php echo $value * $book['book_nprice']; ?></span>
    <h3><?php echo $book['book_name']; ?> by <?php echo $book['book_author']; ?></h3>
    Price: Rs. <?php echo $book['book_nprice']; ?><br /><br />
    Qty: <input type="number" name="qty_<?php echo $book['book_id']; ?>" maxlength="3" size="6" min="1" max="100" value="<?php echo $value; ?>" /><br />
</li>
<?php } echo "<span class=\"cart-price\">Total amount: $total</span>" ?>
<br />
<input type="submit" name="update" value="Update Cart" />
</form></ul></div>

<?php include './template/footer.html'; ?>

按下更新按钮后的示例输出如下：

Original array:
Array (
    [9] => 6
    [8] => 7
    [3] => 8
)

$key => $value for this iteration: 9 => 6
Array (
    [9] => 6
    [8] => 7
    [3] => 6
)

$key => $value for this iteration: 8 => 7 
Array (
    [9] => 6
    [8] => 7
    [3] => 7
)

$key => $value for this iteration: 3 => 7 
Array (
    [9] => 6
    [8] => 7
    [3] => 7 
)

最后一个索引的值在每次迭代中都会更改当前索引的值。这导致最后一个值输出具有与倒数第二个索引相同的值。

帮助？

Answer 1

您之前使用&$value作为参考：

foreach($_SESSION['cart'] as $key => &$value)

变量继续作为循环之外的参考存在，在循环中再次使用它具有预期但非明显的副作用。这甚至在一个大红框in the manual中提到。在第一个循环之后unset($value)以避免这种情况。

Answer 2

您在这里使用引用：

foreach($_SESSION['cart'] as $key => &$value)

要么在此处不使用引用，要么在循环后立即取消设置$ value。

Foreach给出了错误的$ value

2 个答案: