How to include a variable when including a page (PHP)

Question

I have developed a shopping cart that submits the order total amount as a hidden variable across pages as the user selects options throughout the checkout process. On the last page, where the user inputs his/her credit card information, I require that the user check a Terms of Use box. If the user does not select the box, an error message is displayed along with the last checkout page beneath it.

Unfortunately, if I use include(page.php) to display the checkout page, the order amount is $0.00 because it is not including the order total that I have been passing across pages. Is there a way to get the value of that variable to show up on the page? Or is there a better way to display the error message than to use echo for the message and then include to display the page beneath it? I need to be able to point out the error and still have the order total display on the page.

Thanks!

Answer 1

It's not recommended to pass such an important variable via user submitted data; doing this may cause users to pay less than what they're supposed to pay.

A better approach is to store this value inside a session , ie

session_start();
// update the total
$_SESSION['total'] = 123;

Then, in the checkout page:

session_start();
echo "Total: ", $_SESSION['total'];

Sessions are perpetuated with session cookies, comprising a session identifier; at each request the cookie is sent along with the request, so that the system can locate the actual data on disc (or another storage medium).

Note that session_start() must be run before any output is sent to the browser.