This may be a daft question but I keep getting notices on undefined indexes
I'm sorry to tell you, but this implies bad programming-practice. ;)
First off: Leveling the error_reporting in the php-ini is NOT a good idea! Have you ever tested osCommerce with error_reporting set to E_ALL? You better don't!
So get used to write your applications in error_reporting E_ALL, because this will inform you of every not properly intialized var you are using.
Back to the index-problem:
The best way to check the indizes is:
$p = isset($myArray['this_index_doesnt_even_exist']) ? $myArray['this_index_doesnt_even_exist'] : null;
This will check if the index in the given array exists: If, the value will be assigned to the var $p, else null will be returned, thus $p holding null (or any other value you want to assign per default). This will prevend error-output. For more information read the isset()-entry in the official php manual.
However, if you are using a third party app and want to get rid of this annoying messages, you can tell php not to output E_NOTICE or E_WARNING levelled messages. You can do this by editing the php.ini-parameter "error_reporting". But basically, this is something you should never ever do. Your code should run clean even with error_reporting set to E_ALL.
Best regards
Thorsten Suckow-Homberg