Using Bitwise operators on flags

Question

I have four flags

Current = 0x1  
Past = 0x2  
Future = 0x4  
All = 0x7

Say I receive the two flags Past and Future (setFlags(PAST

Answer 1

(value & Current) == Current

Answer 2

If you use .NET 4 or later I prefer to do this, cleaner imao:

[Flags]
public enum Time
{
    None = 0
    Current = 1,
    Past = 2,
    Future = 4
}

myProp = Time.Past | Time.Future;

if (myProp.HasFlag(Time.Past))
{
    // Past is set...
}

Answer 3

you could use AND on it and check if the result is the same as you and with?

Answer 4

First of all - use enums with FlagAttribute. That's what it's for.

[Flags]
public enum Time
{
    None = 0
    Current = 1,
    Past = 2,
    Future = 4
    All = 7
}

Testing then is done like this:

if ( (x & Time.Past) != 0 )

Or this:

if ( (x & Time.Past) == Time.Past )

The latter will work better if "Past" was a combination of flags and you wanted to test them all.

Setting is like this:

x |= Time.Past;

Unsetting is like this:

x &= ~Time.Past;

Answer 5

You may also want to add an extension method like this

  enum states {
     Current = 0x1,
     Past = 0x2,
     Future = 0x4,
     All = 0x7
  };

  static bool Is(this states current, states value) {
     return (current & value) == value;
  }

then you can do:

 if(state.Is(states.Past)) {
    // Past
 }

Answer 6

An addendum to Marc Gravell and Vilx-'s answer:

Your flagged enum shouldn't specify the amount for "All", it should just include your existing values. This goes for any calculated values.

[Flags]
public enum Time
{
    None = 0,
    Current = 1,
    Past = 2,
    Future = 4,
    All = Current | Past | Future
}

Note that Vilx- removed the use of Hexadecimal for values. This is important because once you're past 0x8, your values will have to comply with Hex. You should just stay in decimal.

EDIT: I also want to add that you can use bit shifting rather than hex/decimal.

This looks like:

[Flags]
public enum Time
{
    None = 0,
    Current = 1,
    Past = 1 << 1, // 2, 10 binary
    Future = 1 << 2, // 4, 100 binary
    All = Current | Past | Future
}