void HandleError(char *func, int numArgs, int errorArg, SV *errorSV, int errorCode)
{
    if (numArgs==errorArg+1 && !SvREADONLY(errorSV)) {
        // new interface: set return code
        sv_setiv(errorSV, errorCode);
    } else {
        // old interface: die with error code and deprecation notification
        croak("%s() failed with error %d. The interface now has an additional optional argument.", func, errorCode);
    }
}