Reputation: 32721
Where does this session come from?
I have a header.html which start with session_start();. Then the following code, $_SESSION['cart'][$sw_id] is not set, but suddenly came out. Q1. Can you start session in this way? Q2. How come you can increment quantity of purchase with $_SESSION['cart'][$sw_id]++? It seems to me incrementing id number.
<?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');
?>
Upvotes: 1
Views: 317
Answers (3)
Reputation: 63445
When you call $_SESSION['cart'][$sw_id]++, you are incrementing the value stored at $_SESSION['cart'][$sw_id], which happens to represent the quantity.
If you were updating the product ID, it would look like $sw_id++.
As for the first part of your question, I'm not entirely sure what you're asking. session_start() simply "starts" or activates the session for use. Once called, it will populate the $_SESSION superglobal with the values stored in the session.
Upvotes: 0
Reputation: 15872
A1. Your session starts when you call session_start(). Although a certain variable may not be set in $_SESSION, the session is still initiated.
A2. If you look closely at the code, you'll see that it checks whether $_SESSION['cart'][$sw_id] is set yet. If it is, it uses the ++ operator. If not, it initializes it with a value of 1.
As an aside, you can initialize a variable with ++ in PHP. If the variable or array key is not initialized, PHP assumes it has a starting value of 0.
Upvotes: 4
Reputation: 20456
A1. Yes you can start a session this way. PHP instantiates session keys the same way it instantiates any other variable.
A2. When you do $_SESSION['cart'][$sw_id]++, you're saying add 1 to the value, not to the key. In other words if $array[0]==5 and you do $array[0]++, you get 6, not $array[1].
Upvotes: 0