我有一个以session_start（）;开头的header.html。 然后下面的代码，$ _SESSION ['cart'] [$ sw_id]没有设置，但突然出现了。 Q1。你能用这种方式开始会话吗？ Q2。你怎么能用$ _SESSION ['cart'] [$ sw_id] ++增加购买数量？ 在我看来，增加身份证号码。
<?php # Script 5.7 - cart.php
/*
* This is the shopping cart page.
* This page has two modes:
* - add a product to the cart
* - update the cart
* The page shows the cart as a form for updating quantities.
*/
// Require the configuration file before any PHP code:
require_once ('./includes/config.inc.php');
// Include the header file:
$page_title = 'Shopping Cart';
include_once ('./includes/header.html');
echo '<h1>View Your Shopping Cart</h1>';
// This page will either add to or update the
// shopping cart, based upon the value of $_REQUEST['do'];
if (isset($_REQUEST['do']) && ($_REQUEST['do'] == 'add') ) { // Add new item.
if (isset($_GET['sw_id'])) { // Check for a product ID.
// Typecast to an integer:
$sw_id = (int) $_GET['sw_id'];
// If it's a positive integer,
// get the item information:
if ($sw_id > 0) {
// Define and execute the query:
$q = "SELECT name, color, size FROM general_widgets LEFT JOIN specific_widgets USING (gw_id) LEFT JOIN colors USING (color_id) LEFT JOIN sizes USING (size_id) WHERE sw_id=$sw_id";
$r = mysqli_query($dbc, $q);
if (mysqli_num_rows($r) == 1) {
// Get the information:
list ($name, $color, $size) = mysqli_fetch_array($r, MYSQLI_NUM);
// If the cart already contains
// one of these widgets, increment the quantity:
if (isset($_SESSION['cart'][$sw_id])) {
$_SESSION['cart'][$sw_id]++;
// Display a message:
echo "<p>Another copy of '$name' in color $color, size $size has been added to your shopping cart.</p>\n";
} else { // New to the cart.
// Add to the cart.
$_SESSION['cart'][$sw_id] = 1;
// Display a message:
echo "<p>The widget '$name' in color $color, size $size has been added to your shopping cart.</p>\n";
}
} // End of mysqli_num_rows() IF.
} // End of ($sw_id > 0) IF.
} // End of isset($_GET['sw_id']) IF.
} elseif (isset($_REQUEST['do']) && ($_REQUEST['do'] == 'update')) {
// Change any quantities...
// $k is the product ID.
// $v is the new quantity.
foreach ($_POST['qty'] as $k => $v) {
// Must be integers!
$pid = (int) $k;
$qty = (int) $v;
if ($qty == 0) { // Delete item.
unset ($_SESSION['cart'][$pid]);
} elseif ($qty > 0) { // Change quantity.
$_SESSION['cart'][$pid] = $qty;
}
} // End of FOREACH.
// Print a message.
echo '<p>Your shopping cart has been updated.</p>';
} // End of $_REQUEST IF-ELSE.
// Show the shopping cart if it's not empty:
if (isset($_SESSION['cart']) && !empty($_SESSION['cart'])) {
// Retrieve all of the information for the products in the cart:
$q = "SELECT sw_id, name, color, size, default_price, price FROM general_widgets LEFT JOIN specific_widgets USING (gw_id) LEFT JOIN colors USING (color_id) LEFT JOIN sizes USING (size_id) WHERE sw_id IN (";
// Add each product ID.
foreach ($_SESSION['cart'] as $sw_id => $v) {
$q .= (int) $sw_id . ',';
}
$q = substr ($q, 0, -1) . ') ORDER BY name, size, color';
$r = mysqli_query ($dbc, $q);
if (mysqli_num_rows($r) > 0) {
// Create a table and a form:
echo '<table border="0" width="90%" cellspacing="2" cellpadding="2" align="center">
<tr>
<td align="left" width="20%"><b>Widget</b></td>
<td align="left" width="15%"><b>Size</b></td>
<td align="left" width="15%"><b>Color</b></td>
<td align="right" width="15%"><b>Price</b></td>
<td align="center" width="10%"><b>Qty</b></td>
<td align="right" width="15%"><b>Total Price</b></td>
</tr>
<form action="cart.php" method="post">
<input type="hidden" name="do" value="update" />
';
// Print each item:
$total = 0; // Total cost of the order.
while ($row = mysqli_fetch_array ($r, MYSQLI_ASSOC)) {
// Determine the price:
$price = (empty($row['price'])) ? $row['default_price'] : $row['price'];
// Calculate the total and sub-totals:
$subtotal = $_SESSION['cart'][$row['sw_id']] * $price;
$total += $subtotal;
$subtotal = number_format($subtotal, 2);
// Print the row:
echo <<<EOT
<tr>
<td align="left">{$row['name']}</td>
<td align="left">{$row['size']}</td>
<td align="left">{$row['color']}</td>
<td align="right">\$$price</td>
<td align="center"><input type="text" size="3" name="qty[{$row['sw_id']}]" value="{$_SESSION['cart'][$row['sw_id']]}" /></td>
<td align="right">\$$subtotal</td>
</tr>\n
EOT;
} // End of the WHILE loop.
// Print the footer, close the table, and the form:
echo ' <tr>
<td colspan="5" align="right"><b>Total:</b></td>
<td align="right">$' . number_format ($total, 2) . '</td>
</tr>
<tr>
<td colspan="6" align="center">Set an item\'s quantity to 0 to remove it from your cart.</td>
</tr>
</table><div align="center"><button type="submit" name="submit" value="update">Update Cart</button>
<a href="checkout.php"><button type="button" name="checkout" value="Checkout">Checkout</button></a></div>
</form>';
} // End of mysqli_num_rows() IF.
} else {
echo '<p>Your cart is currently empty.</p>';
}
// Include the footer file to complete the template:
include_once ('./includes/footer.html');
?>
答案 0 :(得分：4)
A1。当您致电session_start()时，您的会话就会开始。虽然$ _SESSION中可能未设置某个变量，但会话仍在启动。
A2。如果仔细查看代码，您会看到它检查是否已设置$_SESSION['cart'][$sw_id]。如果是，则使用++运算符。如果没有，则使用值1初始化它。
另外，您可以在PHP中使用++初始化变量。如果未初始化变量或数组键，则PHP假定其起始值为0。
答案 1 :(得分：0)
A1。 是的，你可以用这种方式开始一个会话。 PHP以实例化任何其他变量的方式实例化会话密钥。
A2。 当你执行$ _SESSION ['cart'] [$ sw_id] ++时，你说的是将值加1，而不是键。换句话说，如果$ array [0] == 5并且你执行$ array [0] ++，你得到6，而不是$ array [1]。
答案 2 :(得分：0)
当您致电$_SESSION['cart'][$sw_id]++时，您正在递增$_SESSION['cart'][$sw_id]处存储的值，这恰好代表数量。
如果您要更新产品ID，它看起来像$sw_id++。
关于你问题的第一部分，我不完全确定你在问什么。 session_start()只需“启动”或激活会话即可使用。一旦被调用，它将使用存储在会话中的值填充$_SESSION超全局。