Is there a pattern or a method in C# to check if an (int 1,2,4,8,...) option is true or false

Question

I like to write enum or integer to pass option to my methods. Is there a pattern or a method in C# to check if an (int 1,2,4,8,...) option is true or false. I think it should easily be possible via binary functions.

class Program
{
    public enum Option
    {
        Option_A = 1,
        Option_B = 2,
        Option_C = 4,
        Option_D = 8,
    }

    static void Main(string[] args)
    {
        int activeOption = 5; // Means I activeted the Option_A and Option_C
        if (IsOption(activeOption, Option.Option_A)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_B)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_C)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_D)) { /*do work*/ }
    }

    private static bool IsOption(int activeOption, Option option)
    {
        /*Evaluate if IsOption is true or false*/
        throw new NotImplementedException();
    }
}

EDIT

Am I limited the number of options that I can create like this?

@Martinho if you look at the code sample, it is required that multiple options be selectable. An int is more space-efficient than a collection of Options. — Robin Green, May 20 '11 at 09:25
@Robin: An Option enum is as space-efficient as an int. Guess why: it's actually an int. — R. Martinho Fernandes, May 20 '11 at 09:27
@Dan you misspelled Martinho's name, so he might not see your question. The Option enum is the thing in *your code* called Option! — Robin Green, May 20 '11 at 09:32
Am I limited the number of options that I can create like this? — Bastien Vandamme, May 20 '11 at 09:53

score 10 · Accepted Answer · edited May 23 '17 at 12:04

Since your enum contains flags (or if you prefer, is a bitfield), you should add a FlagsAttribute to it:

[Flags]
public enum Option
{
    Option_A = 1,
    Option_B = 2,
    Option_C = 4,
    Option_D = 8,
}

And then, checking is typically done with the bitwise and operator. A cast will also be needed, because you are using an int variable.

if(((Option)activeOption & Option.Option_A) != Option.Option_A) //...

If you want to encapsulate this nastiness away, check out the article linked in Smudge202's answer. If you are running .NET 4, you don't even need to do that: check sehe's answer.

But you should really try using a variable of type Option directly, and combine the options with the bitwise or operator:

Option activeOption = Option.Option_A | Option.Option_C;

Of course using this scheme limits the number of options you can create. If you leave it as is, you can only create 32 different options, because an int (the default underlying type of an enum) has only 32-bits. If you use a long you can have 64 different options:

[Flags]
public enum Option : long
{
    Option_A = 1,
    Option_B = 2,
    Option_C = 4,
    Option_D = 8,
    // blah blah
}

However, if you need an arbitrary number of options, it's probably time to change strategies. You could make a custom type that behaves like an enum, but you'll probably be better off with just a regular, non-flags enum, and a HashSet<Option>.

public enum Option
{
    Option_A = 1, // notice the sequential values now
    Option_B = 2,
    Option_C = 3,
    Option_D = 4,
}

HashSet<Option> options = new HashSet<Option> { Option.Option_A, Option.Option_C };
if(options.Contains(Option.Option_A)) // ...

+1 for flags attribute. The [link I posted](http://www.codeproject.com/Articles/37921/Enums-Flags-and-Csharp-Oh-my-bad-pun.aspx) as an answer shows an extension method you can use to simplify the code writing when testing for enum members which hopefully compliments your answer. — Smudge202, May 20 '11 at 09:31
It will complement the answer. Also, [C# 4.0 will complement it](http://stackoverflow.com/questions/6069869/is-there-a-pattern-or-a-method-in-c-to-check-if-an-int-1-2-4-8-option-is-t/6070172#6070172) — sehe, May 20 '11 at 09:50
@Martinho Am I limited the number of options that I can create like this? — Bastien Vandamme, May 20 '11 at 09:56
@Dran: see my edit. Also thanks @Smudge and @sehe. I mentioned your answers in mine. — R. Martinho Fernandes, May 20 '11 at 10:00
@Martinho Thank you very much for this well documented answer — Bastien Vandamme, May 20 '11 at 10:03
@Dran: glad to be of help. Also note my last edit. There was a corner case that I forget in there, and my check could fail (I'll leave out the how and why as an exercise for the reader). — R. Martinho Fernandes, May 20 '11 at 10:11

BoltClock · Answer 2 · 2011-05-20T09:47:47.583

3

Use bitwise AND to check if the bits in option are set in activeOption. You also need to make both parameters the same type so the operator will work (you are checking the bits in an Option bitmask anyway):

private static bool IsOption(Option activeOption, Option option)
{
    return (activeOption & option) == option;
}

edited May 20 '11 at 09:47

answered May 20 '11 at 09:23

BoltClock

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I get an error --> Operator '&' cannot be applied to operands of type 'int' – Bastien Vandamme May 20 '11 at 09:26
@Dran Dane: You need to change your method sig so both parameters are of the same type. – BoltClock May 20 '11 at 09:26
Am I limited the number of options that I can create like this? – Bastien Vandamme May 20 '11 at 09:56

score 2 · Answer 3 · answered May 20 '11 at 09:48

In addition to FlagsAttribute mentioned, in C# there is the Enum.HasFlag Method

using System;

[Flags] public enum DinnerItems {
   None = 0,
   Entree = 1,
   Appetizer = 2,
   Side = 4,
   Dessert = 8,
   Beverage = 16, 
   BarBeverage = 32
}

public class Example
{
   public static void Main()
   {
      DinnerItems myOrder = DinnerItems.Appetizer | DinnerItems.Entree |
                            DinnerItems.Beverage | DinnerItems.Dessert;
      DinnerItems flagValue = DinnerItems.Entree | DinnerItems.Beverage;
      Console.WriteLine("{0} includes {1}: {2}", 
                        myOrder, flagValue, myOrder.HasFlag(flagValue));
   }
}
// The example displays the following output:
//    Entree, Appetizer, Dessert, Beverage includes Entree, Beverage: True

score 1 · Answer 4 · answered May 20 '11 at 09:26

1

Take a look at Enumerations that use Flag Attributes.

http://www.codeproject.com/Articles/37921/Enums-Flags-and-Csharp-Oh-my-bad-pun.aspx

answered May 20 '11 at 09:26

Smudge202

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score 1 · Answer 5 · answered May 20 '11 at 13:36

If you are using .NET 4.0 you can use HasFlag.

static void Main(string[] args)
{
    Option activeOption = (Option)5; // Means I activeted the Option_A and Option_C
    if (activeOption.HasFlag(Option.Option_A)) { /*do work*/ }
    if (activeOption.HasFlag(Option.Option_B)) { /*do work*/ }
    if (activeOption.HasFlag(Option.Option_C)) { /*do work*/ }
    if (activeOption.HasFlag(Option.Option_D)) { /*do work*/ }
}

Is there a pattern or a method in C# to check if an (int 1,2,4,8,...) option is true or false

5 Answers5