use of sessions compared to global scope

hi guys , as per my previous email i am trying to sort out a similar error handling as c or java exception, although in the error handler i am sending an error code to it and then return to the previous page with the error on it , the only way i can do this is to store the code in a session variable , i have just realised i can also do this by $_GLOBALS['error_code'] , which is a more efficient way to do this