undefined index from different carts

I have 4 different pages with add to cart buttons that all sent different session variables to the same "display manager" page. Is there 1 place that I could php code something like this to stop the error:

<?php
if(isset($_SESSION['cost'])){
$_SESSION['cost'] = $_SESSION['cost'];}
else
{ $_SESSION['cost'] = "";}
?>


I tried placing this code in display manager and in "WA_eCart\ eCart.php and still I get the below error. Because different data is sent from the different pages I get the following error for this particular variable. Thanks


Notice: Undefined index: cost in C:\wamp\www\Long Multi Shores\WA_eCart\ambCart_PHP.php on line 301

Generally speaking when I'm checking if a variable is set I also check it to see if it is "" like this:

if(isset($_SESSION['cost']) && $_SESSION['cost'] != ""){

This will ensure that the variable is set and not empty. Along with this any time you are using a session variable on a page you will need to ensure that the session has been started, you can do that with some code like this:

if(!session_id())session_start();

This is a one line if statement checking for the session id, if it is not there then the session is started.

I placed the code at the top of the "display manager" page but still get the same message. Is there somewhere else I should place this code so that when the session variable is not sent, there will not be an error message. Below is the code I changed to. Thanks

<?php
// start session varible
if (!isset($_SESSION)) {
session_start();
}
?>
<?php
if(isset($_SESSION['mthCost']) && $_SESSION['mthCost'] != "") {
$mthCost = $_SESSION['mthCost'];}

Any time you get the undefined index message it is because the variable you are making reference to has not been defined. Since the code is a little different on the page the error message should be different also, it should include the exact line number where this is occurring.

If the warning is referring to your $mthCost variable then this could occur any time that the session variable is not set or is empty, this $mthCost variable will not get a value. If you make reference to this variable anywhere on the page then you can get this error if the variable has not been defined.

If you are printing out the variable anywhere on the page you can add in a check to make sure it is set like this:

[php[
<?php echo isset($mthCost)?$mthCost:"" ?>
[/php]

This will print the value if it is set, otherwise it will print nothing.

For starting the session you should make the check like this:

if(!session_id())session_start();