Most common C# bitwise operations on enums

Question

For the life of me, I can't remember how to set, delete, toggle or test a bit in a bitfield. Either I'm unsure or I mix them up because I rarely need these. So a "bit-cheat-sheet" would be nice to have.

For example:

flags = flags | FlagsEnum.Bit4;  // Set bit 4.

or

if ((flags & FlagsEnum.Bit4)) == FlagsEnum.Bit4) // Is there a less verbose way?

Can you give examples of all the other common operations, preferably in C# syntax using a [Flags] enum?

Answer 1

I did some more work on these extensions - You can find the code here

I wrote some extension methods that extend System.Enum that I use often... I'm not claiming that they are bulletproof, but they have helped... Comments removed...

namespace Enum.Extensions {

    public static class EnumerationExtensions {

        public static bool Has<T>(this System.Enum type, T value) {
            try {
                return (((int)(object)type & (int)(object)value) == (int)(object)value);
            } 
            catch {
                return false;
            }
        }

        public static bool Is<T>(this System.Enum type, T value) {
            try {
                return (int)(object)type == (int)(object)value;
            }
            catch {
                return false;
            }    
        }


        public static T Add<T>(this System.Enum type, T value) {
            try {
                return (T)(object)(((int)(object)type | (int)(object)value));
            }
            catch(Exception ex) {
                throw new ArgumentException(
                    string.Format(
                        "Could not append value from enumerated type '{0}'.",
                        typeof(T).Name
                        ), ex);
            }    
        }


        public static T Remove<T>(this System.Enum type, T value) {
            try {
                return (T)(object)(((int)(object)type & ~(int)(object)value));
            }
            catch (Exception ex) {
                throw new ArgumentException(
                    string.Format(
                        "Could not remove value from enumerated type '{0}'.",
                        typeof(T).Name
                        ), ex);
            }  
        }

    }
}

Then they are used like the following

SomeType value = SomeType.Grapes;
bool isGrapes = value.Is(SomeType.Grapes); //true
bool hasGrapes = value.Has(SomeType.Grapes); //true

value = value.Add(SomeType.Oranges);
value = value.Add(SomeType.Apples);
value = value.Remove(SomeType.Grapes);

bool hasOranges = value.Has(SomeType.Oranges); //true
bool isApples = value.Is(SomeType.Apples); //false
bool hasGrapes = value.Has(SomeType.Grapes); //false

Answer 2

C++ syntax, assuming bit 0 is LSB, assuming flags is unsigned long:

Check if Set:

flags & (1UL << (bit to test# - 1))

Check if not set:

invert test !(flag & (...))

Set:

flag |= (1UL << (bit to set# - 1))

Clear:

flag &= ~(1UL << (bit to clear# - 1))

Toggle:

flag ^= (1UL << (bit to set# - 1))

Answer 3

C++ operations are: & | ^ ~ (for and, or, xor and not bitwise operations). Also of interest are >> and <<, which are bitshift operations.

So, to test for a bit being set in a flag, you would use: if (flags & 8) //tests bit 4 has been set