PHP 2D array fails to increment qty - php

Question

I have a problem updating a multidimensional array in PHP. I'm trying to implement am e-commerce website for a project and I am having problems with the shopping cart implementation.
Basically, I use a session to track the items the user adds to the shopping cart. Here's my logic in plain Pseudo code that is executed once the user clicks the add button after specifying a quantity to add for a product:
RETRIEVE 'cartItems' 2D array from SESSION array
IF 'cartItems' array does not exist in the session create new empty array and add the cartItem sub array to it with the qty and productID
ELSE Loop through the array retrieved from the SESSION array, find the product ID that matches the given product ID (index 0) and update the qty for that subarray (index 1).
Here is my PHP script addToCart.php which in turn calls another function in another script file that is included in it:
<?php
require_once("cart_utility.php");
session_start();
// Script for adding a given product to the client's cart through the use of Ajax and sessions
// retrieve values from ajax request
$productID = $_GET["productID"];
$qty = $_GET["qty"];
$cartItems = null;
// use sessions to add the items to the user's cart
// retrieve the multi-dimensional cart array if it exists, otherwise create one and add it
if(isset($_SESSION["cartItems"])){
$cartItems = $_SESSION["cartItems"];
}
else{
$cartItems = array();
}
addQtyForProduct($productID, $qty, $cartItems);
$_SESSION["cartItems"] = $cartItems;
print "Session cartItems after function return: ";
var_dump($_SESSION["cartItems"]);
// return info string with new qty of cart items
print ("success-" . getTotalCartItems($cartItems));
?>
And here's the other script file that does the handling of inserting and updating the array:
<?php
// Utility functions for retrieving items from the 2D cart items array
/* The array structure is given as (example values):
* | productID | qty |
* 0 | 1 | 3 |
* 1 | 2 | 1 |
* 2 | 5 | 8 |
* 3 | 8 | 3 |
*/
// increments the qty for the given product. If it does not exist then it is added into the main session array
// $cartItems: the main 2D array with the structure given above, pass by reference to change the array
function addQtyForProduct($productID, $qty, &$cartItems)
{
foreach($cartItems as $cartItem)
{
var_dump($cartItem);
if($cartItem[0] == $productID){
//print "Quantity given to increment: $qty";
//var_dump($cartItem);
print "Qty in current session array: $cartItem[1]";
$cartItem[1] += $qty;
print "New qty in cartItem array: $cartItem[1]";
return;
}
}
// not found, therefore add it to the main items array
array_push($cartItems, array($productID, $qty));
}
// returns the total number of items in the cart
function getTotalCartItems($cartItems)
{
$total = 0;
foreach($cartItems as $cartItem)
$total += $cartItem[1];
return $total;
}
?>
I have placed some var_dump statements and can confirm that upon returning from the function 'addQtyForProduct', the array is not updated. But why? I pass the array by reference to directly alter it's contents.
It successfully adds on the first time when there is no existing array but fails to increment if the array exists.
Also, the values are successfully incremented in the 'addQtyForProduct' function but the array somehow is not updated when it returns from the function.
I would gladly appreciate some help on this. I've been trying to understand this for days now and It's driving me nuts.

Answer 1

As read on this page you should use references. Add a & in front of your $cartItem and your script should work. Right now PHP stores a 'copy' of every value in your array in $cartItem, rather than it's reference. So currently you are editing a copy of the original, rather than the original array.