urgent php cookie kill problem

[jas168]

Hi i have a problem trying to kill a cookie session below is the codes i create the cookie

function GetCartId()
{
// This function will generate an encrypted string and
// will set it as a cookie using set_cookie. This will
// also be used as the cookieId field in the cart table

if(isset($COOKIE["cartId"]))
{
return $COOKIE["cartId"];
}
else
{
// There is no cookie set. We will set the cookie
// and return the value of the users session ID

session_start();
setcookie("cartId", session_id(), time() + ((3600 24) 30));
return session_id();
}
}

i just want to kill this cookie i have try so many ways but no luck
<?php
setcookie("cartId", "", time() - ((3600 24) 2));

?>

any ideas..

thanks advance