c# flag comparison "only contain" a set

Question

[ Flags ]
public enum StatusType { a,b,c,d,e,f,g }

StatusType m_StatusType = a | b;

If ( m_StatusType only contains a and b )  // I need help here
{ 

}

Hi,

I need some help on comparing flags. How can I know if a flag enum variable contains only some particular values?

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. — Roman Marusyk, Aug 18 '16 at 23:36
Please see the marked duplicate for a _thorough_ discussion of enum types that use `[Flags]` and how to use them. If you find yourself with some remaining confusion, post a new question that includes a good [mcve] that shows clearly what trouble you're having. Describe what the code does, what you want it to do instead, and what _specifically_ you're having trouble figuring out. — Peter Duniho, Aug 18 '16 at 23:42
@DVN then Peter is right and you should read this http://stackoverflow.com/questions/8447/what-does-the-flags-enum-attribute-mean-in-c — Gerardo Grignoli, Aug 18 '16 at 23:47

score 1 · Answer 1 · answered Aug 18 '16 at 23:38

First off, when defining a flags enum, each flag should represent a single bit in the enum:

enum X { a = 1, b = 2, c = 4, d = 8 }

This allows you to combine flags as well:

CandD = 12, //has both c and d flags set.

Or if you have a lot of them:

enum X { 
  a = 1 << 0, 
  b = 1 << 1, 
  c = 1 << 2, 
  d = 1 << 3,
  ...
  CAndD = c | d
}

You can use a simple equality comparison to test if only certain flags are set.

public bool ContainsOnly(X value, X flags) 
{
     return value == flags;
}

public bool ContainsOnlyCandD(X value) 
{
     return value == (X.c | X.d);
}

public bool ContainsBothCandDButCouldContainOtherStuffAsWell(X value) 
{
     return (value & (X.c | X.d)) == (X.c | X.d);
}

score 1 · Answer 2 · answered Aug 18 '16 at 23:39

1

Firstly, your flags should be created as such:

[Flags]
public enum StatusType
{
    None = 0
    A = 1,
    B = 2,
    C = 4,
    D = 8,
    E = 16,
    F = 32,
    G = 64
}

You can then assign as such:

var statusType = StatusType.A | StatusType.B;

And test it as such:

if (statusType.HasFlag(StatusType.A))
{
    //A is defined
}

answered Aug 18 '16 at 23:39

João Lourenço

736
5
8

I just want to elaborate on why this answer works, for OP's benefit (and any future people). Each of those enum values are being assigned a value in binary that only contains a single 1, and the rest are 0. `1 = 1, 2 = 01, 4 = 100, 8 = 1000, 16 = 10000, etc`. `|` is the bitwise or operator, and doing something like `1 | 4` yields the binary number `101`. You can then compare them using bitwise and `&` to see if the value is present. `101 & 10 = 000`, but `101 & 100 = 100`. Hopefully the other explanations on this page make more sense. – Cody Aug 18 '16 at 23:46

c# flag comparison "only contain" a set

2 Answers2