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

if ((flags & PAST) == PAST)
{
  // PAST is there
}

if ((flags & CURRENT) != CURRENT)
{
  // CURRENT is not there
}

Answer 2

I think what is missing is to take "all" but one

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

Then with the above flags enum, you can do

var notNow= Time&~Time.Current;

Answer 3

If you want all bits in the test mask to match:

if((value & mask) == mask) {...}

If you want any single bit in the test mask to match:

if((value & mask) != 0) {...}

The difference is most apparent when you are testing a value for multiple things.

To test for exclusion:

if ((value & mask) == 0) { }