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Enum to Array

Posted on 2009-07-16
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Last Modified: 2013-12-17
Hello,

If I have an enum like this...

public enum Things : int
{
      A = 1,
      B = 2,
      C = 4,
      D = 8.
      E = 16,
      F = 32
}


How can I then convert an int value of 11 (for example) into a Thing[] array which would contain Thing.A, Thing.B and Thing.D (1+2+8 = 11)

Cheers.

ETFairFax
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Question by:ETFairfax
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6 Comments
 
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Expert Comment

by:happel
ID: 24868014
I think you have to test for the bitflags and create/fill the array in a custom function.
Don't know a framework function which does this for you.

As bit test function I use they attached snippet..


        public static Boolean IsBitSet(Object bitField, Object checkBit)
        {
            return (((byte)(int)bitField & (byte)(int)checkBit) == (byte)(int)checkBit);
        }

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LVL 39

Expert Comment

by:abel
ID: 24868055
It is actually much simpler then what happel proposes. You can use the FlagsAttribute and simply cast the value. The following statement prints "A, B, D":

[Flags()]
private enum MyTestEnum
{
    None = 0,
    A = 1, B = 2, C = 4, D = 8, E = 16, F = 32
}
 
private void testEnum()
{
    myTestEnum testEnum = (MyTestEnum) 11;
    Debug.WriteLine(testEnum);
}

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Accepted Solution

by:
abel earned 125 total points
ID: 24868215
About using the Flags attribute:
 
 1. You should assign the values as powers of 2
 2. You should always assign "None = 0"
 3. Each enum variable of Flags type can have multiple values (flags)
 4. You can test flags with | (OR), & (AND) and ^ (XOR) as you would in any language
 5. Same for assignment
 6. You can use foreach or make it an array as follows:

// NOTE: this only works with the FlagsAttribute set on the enum!
 
// .NET 2.0 version:
private int[] EnumToArray(Enum someEnum)
{
    List<int> list = new List<int>();
    foreach (var it in Enum.GetValues(someEnum.GetType()))
    {
        if ((Convert.ToInt32(it) & Convert.ToInt32(someEnum)) != 0)
            list.Add((int)it);
    }
    return list.ToArray();
}
 
// .NET 3.5 version:
private int[] EnumToArray(Enum someEnum)
{
    return (from int en in Enum.GetValues(someEnum.GetType())
           where (en & Convert.ToInt32(someEnum)) != 0
           select en).ToArray();
}

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Author Closing Comment

by:ETFairfax
ID: 31604158
Excellent.  Very informative.  Ta very much!!
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LVL 39

Expert Comment

by:abel
ID: 24868297
If you are lucky enough to be able to use .NET 3.5, consider creating an extension function for the Enum type, you can then use it for every Enum type in the same manner you are used to with other types that support Enumeration. Below is an example of a ToArray() extension function. You can call it like:

MyTestEnum someEnum = (MyTestEnum) 11;
int[] someArray = someEnum.ToArray();

This is of course the same idea, just a bit more convenient. ;-)

public static class EnumExtensions
{
    public static int[] ToArray(this Enum someEnum)
    {
        return (from int en in Enum.GetValues(someEnum.GetType())
                where (en & Convert.ToInt32(someEnum)) != 0
                select en).ToArray();
    }
}

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LVL 39

Expert Comment

by:abel
ID: 24868301
Thanks for the follow up & the compliment!
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