Comparing flags with flags - check for matches

Question

Say I have an enum:

[Flags]
public enum Alpha
{
    NULL = 0,
    A0 = 1,
    A1 = 2,
    A2 = 4,
    A3 = 8
}

And I have the following:

Alpha selected = A0 | A1 | A2

Alpha compare = A1 | A3

I want to check if any of the selected flags are also in the compare flags.

The only way I can think to do this so far is (pseudocode)

foreach(Alpha flag in Enum.GetValues(typeof(Alpha)))
{
    if (selected.HasFlag(flag) && compare.HasFlag(flag))
    {
        return true
    }
}
return false

Is there a more logic-al way to do this?

Orel Eraki · Accepted Answer · 2015-11-20T12:23:23.553

2

Because it is treated as bit field, you can use it in the same fashion.

FlagsAttribute Class

Indicates that an enumeration can be treated as a bit field; that is, a set of flags

bool result = (selected & compare) > 0; // First solution
bool result2 = (selected & compare).Any(); // Second solution

edited Nov 20 '15 at 12:23

answered Nov 20 '15 at 12:09

Orel Eraki

11,940
3
28
36

1

This answer is producing incorrect results. It checks whether ALL the flags in "selected" exists in "compare". Did you test your answer with selected = A1|A2|A3 and compare = A1|A3 ? It evaluates to false. – Oguz Ozgul Nov 20 '15 at 12:21
1

Fix. Sorry my bad, thought he wanted to check if all of the flags exists and not only if one flag exists. Thanks for the comment. – Orel Eraki Nov 20 '15 at 12:23
2

No problem. The very first thing we need to make sure is to get the requirements right :) – Oguz Ozgul Nov 20 '15 at 12:27
Where does `.Any()` come in? I don't get the option in intellisense – simonalexander2005 Nov 20 '15 at 13:50
@simon it is an extension method. Just add using System.Linq; – Oguz Ozgul Nov 20 '15 at 14:33
I am using Linq, it's still not there (VS2015) – simonalexander2005 Nov 20 '15 at 14:54

score 1 · Answer 2 · answered Nov 20 '15 at 12:15

1

What you need is probably:

(selected & compare) > 0;

answered Nov 20 '15 at 12:15

Oguz Ozgul

6,809
1
14
26

score 1 · Answer 3 · answered Nov 20 '15 at 12:16

1

When you use an AND operator, any flag which is common between the two operands will be present in the result.

Then you just have to compare and see if the result is greater than Zero:

bool anySelected = (selected & compare) > 0;

answered Nov 20 '15 at 12:16

Alireza

4,976
1
23
36

score 1 · Answer 4 · answered Nov 20 '15 at 12:24

1

I think first you should remove the NULL from the Alpha, then just return (selected & compare) != 0, anyEnum.HasFlag(Alpha.NULL) will always be ture.

answered Nov 20 '15 at 12:24

Norgerman

79
5

Comparing flags with flags - check for matches

4 Answers4