flagsattribute - negative values?

Question

I have a enum with a flagsattribute, which i use to represent permissions. I use it to compare if (CurrentPermissions & Permission1 == Permission1) etc...

[FlagsAttribute]
enum MyPermission
{
  None = 0,
  Permission1 = 1,
  Permission2 = 2,
  Permission3 = 4,
  Permission4 = 8,...
  ..................
  and so on

}

However, we reach a max limit. Can i use negative values like -1, -2, -4 etc. once i run out of enum values ?

Answer 1

You can define entries with any values you like within a Flags enum. Two common ones would be zero and 0xffffffff (-1) because these can be useful values to represent "all options disabled" and "all options enabled" values, e.g

enum DrawingOptions
{
   None         = 0,

   DrawLines    = 1 << 0,
   FillShapes   = 1 << 1,
   Antialias    = 1 << 2,

   BestQuality  = 0xffffffff
}

(If you add a new option, any code that enabled "BestQuality" will automatically have that option enabled, so you won't have to search through your code to update everything)

However, negative numbers other than -1 aren't likely to be very useful, as Frank Bollack has already answered.

You may also have to be rather careful with negative numbers when the size of your enum (byte, int32, int64) changes.