C#

public BASSException() : this(GetErrorCode()){}
internal BASSException(int code) : base(GetErrorDescription((Error)code))
{
  err = (Error) code;
}

public class MyException {
internal enum ErrorCode 
{
  None,
  User,
  Programmer,
  Unknown,
}

static ErrorCode errorcode = ErrorCode.None;

internal static ErrorCode Error
{
  get {
    return errorcode;
  }
  set {errorcode = value;}
}

internal static string GetErrorDescription(ErrorCode code)
{
  switch(code)
  {
  case ErrorCode.User:
    return "User error occured, check blah blah for dohdoh";
  case ErrorCode.Programmer:
    return "Programmer error occured, email blah";
  case ErrorCode.Unknown:
    return "Unknown error occured, no help available";
  case default:
    return "No error";
  }
}

public MyException():this(Error){}
internal MyException(ErrorCode code):base(GetErrorDescription(code))
{
  errorcode = ErrorCode.None; //reset the errorcode, base gets called 1st.
}
}

...
if (somestring == "badstring") 
{
  MyException.Error = Error.User;
  throw new MyException();
}
...

static void CheckString(string str)
{
  if (somestring == "badstring") 
  {
    MyException.Error = Error.User;
    throw new MyException();
  }  
}
...
CheckString("badstring");
...