PHP - Array_key_exists

Hi,

Im encountering this error when i add items to my cart, im using sessions to store my cart items in an array. this error only happens the first time i add something, then if i go clear my session it works and no errors.

Code: [Select]
Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /home/byronhea/public_html/oos/mini-cart.php on line 18
Here is the line its refering to


Code: [Select]
if(array_key_exists($pid, $_SESSION['cart']))

and here is the block of code it belongs to

Code: [Select]
if(!isset($_SESSION))
{
session_start('cart');
}
// Process actions

$pid = $_POST['prodid'];
$q = $_POST['qty'];

if(array_key_exists($pid, $_SESSION['cart']))
{
$_SESSION['cart'][$pid]=$_SESSION['cart'][$pid]+$q;
}
ELSE
{
$_SESSION['cart'][$pid]=$q;
}
Any help would be appreciated.

I'm just wondering if there is a function like array_key_exists that could take an array as the search parameter and check that all keys exist. It would be easy enough to code if I need to but I was hoping it would already exist. All wanted to use it for is a really quick form check to make sure that all the expected values were POSTed before I actually start filtering and validating individual fields.

Thanks in advance for any recommendations