I have four flags
Current = 0x1
Past = 0x2
Future = 0x4
All = 0x7
Say I receive the two flags Past and Future ( setFlags(PAST | FUTURE)
). How can I tell if Past
is in it? Likewise how can I tell that Current
is not in it? That way I don't have to test for every possible combination.
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) { }
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;
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
}
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...
}
if ((flags & PAST) == PAST)
{
// PAST is there
}
if ((flags & CURRENT) != CURRENT)
{
// CURRENT is not there
}
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
}
(value & Current) == Current
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;
I have four flags
Current = 0x1
Past = 0x2
Future = 0x4
All = 0x7
Say I receive the two flags Past and Future ( setFlags(PAST | FUTURE)
). How can I tell if Past
is in it? Likewise how can I tell that Current
is not in it? That way I don't have to test for every possible combination.
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