Array of Error Codes: Key/Values

[<Brendan_Crowley@xxxxxxxxxxxx>]

Hi,

I'm new to php and i'm looking to setup an array (or what work best) of codes and corresponding error strings, for example (pseudo code):
ERROR_CODES = array('-1' => 'Error opening file', '-2' => 'General File IO Error', '-3' => 'Database connection error');

Access these string values using the key codes (negative key values) to formulate a SoapFault, e.g.:
throw new SoapFault('-1', ERROR_CODES[-1], 'actor', 'detail', 'name', 'header');

How best to implement this in php?

Thanks,
Brendan