How to check if any flags of a flag combination are set?

In .NET 4 you can use the Enum.HasFlag method :

using System; [Flags] public enum Pet { None = 0, Dog = 1, Cat = 2, Bird = 4, Rabbit = 8, Other = 16 } public class Example { public static void Main() { // Define three families: one without pets, one with dog + cat and one with a dog only Pet[] petsInFamilies = { Pet.None, Pet.Dog | Pet.Cat, Pet.Dog }; int familiesWithoutPets = 0; int familiesWithDog = 0; foreach (Pet petsInFamily in petsInFamilies) { // Count families that have no pets. if (petsInFamily.Equals(Pet.None)) familiesWithoutPets++; // Of families with pets, count families that have a dog. else if (petsInFamily.HasFlag(Pet.Dog)) familiesWithDog++; } Console.WriteLine("{0} of {1} families in the sample have no pets.", familiesWithoutPets, petsInFamilies.Length); Console.WriteLine("{0} of {1} families in the sample have a dog.", familiesWithDog, petsInFamilies.Length); } } 

The example displays the following output:

// 1 of 3 families in the sample have no pets. // 2 of 3 families in the sample have a dog. 

I use extension methods to write things like that :

if (letter.IsFlagSet(Letter.AB)) ... 

Here's the code :

public static class EnumExtensions { private static void CheckIsEnum<T>(bool withFlags) { if (!typeof(T).IsEnum) throw new ArgumentException(string.Format("Type '{0}' is not an enum", typeof(T).FullName)); if (withFlags && !Attribute.IsDefined(typeof(T), typeof(FlagsAttribute))) throw new ArgumentException(string.Format("Type '{0}' doesn't have the 'Flags' attribute", typeof(T).FullName)); } public static bool IsFlagSet<T>(this T value, T flag) where T : struct { CheckIsEnum<T>(true); long lValue = Convert.ToInt64(value); long lFlag = Convert.ToInt64(flag); return (lValue & lFlag) != 0; } public static IEnumerable<T> GetFlags<T>(this T value) where T : struct { CheckIsEnum<T>(true); foreach (T flag in Enum.GetValues(typeof(T)).Cast<T>()) { if (value.IsFlagSet(flag)) yield return flag; } } public static T SetFlags<T>(this T value, T flags, bool on) where T : struct { CheckIsEnum<T>(true); long lValue = Convert.ToInt64(value); long lFlag = Convert.ToInt64(flags); if (on) { lValue |= lFlag; } else { lValue &= (~lFlag); } return (T)Enum.ToObject(typeof(T), lValue); } public static T SetFlags<T>(this T value, T flags) where T : struct { return value.SetFlags(flags, true); } public static T ClearFlags<T>(this T value, T flags) where T : struct { return value.SetFlags(flags, false); } public static T CombineFlags<T>(this IEnumerable<T> flags) where T : struct { CheckIsEnum<T>(true); long lValue = 0; foreach (T flag in flags) { long lFlag = Convert.ToInt64(flag); lValue |= lFlag; } return (T)Enum.ToObject(typeof(T), lValue); } public static string GetDescription<T>(this T value) where T : struct { CheckIsEnum<T>(false); string name = Enum.GetName(typeof(T), value); if (name != null) { FieldInfo field = typeof(T).GetField(name); if (field != null) { DescriptionAttribute attr = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute)) as DescriptionAttribute; if (attr != null) { return attr.Description; } } } return null; } } 

There is the HasFlag method in .NET 4 or higher.

Check if the letter includes A OR B

letter.HasFlag(Letters.A) || letter.HasFlag(B); 

Check if the letter includes A AND B

letter.HasFlag(Letters.A | Letters.B); 

If you can use .NET 4 or higher than use HasFlag() method

examples

letter.HasFlag(Letters.A | Letters.B) // both A and B must be set 

same as

letter.HasFlag(Letters.AB) 

If it really annoys you, you can write a function like that:

public bool IsSet(Letters value, Letters flag) { return (value & flag) == flag; } if (IsSet(letter, Letters.A)) { // ... } // If you want to check if BOTH Letters.A and Letters.B are set: if (IsSet(letter, Letters.A & Letters.B)) { // ... } // If you want an OR, I'm afraid you will have to be more verbose: if (IsSet(letter, Letters.A) || IsSet(letter, Letters.B)) { // ... } 

To check if for example AB is set I can do this:

if((letter & Letters.AB) == Letters.AB)

Is there a simpler way to check if any of the flags of a combined flag constant are set than the following?

This checks that both A and B are set, and ignores whether any other flags are set.

if((letter & Letters.A) == Letters.A || (letter & Letters.B) == Letters.B) 

This checks that either A or B is set, and ignores whether any other flags are set or not.

This can be simplified to:

if(letter & Letters.AB) 

Here's the C for binary operations; it should be straightforward to apply this to C#:

enum { A = 1, B = 2, C = 4, AB = A | B, All = AB | C, }; int flags = A|C; bool anything_and_a = flags & A; bool only_a = (flags == A); bool a_and_or_c_and_anything_else = flags & (A|C); bool both_ac_and_anything_else = (flags & (A|C)) == (A|C); bool only_a_and_c = (flags == (A|C)); 

Incidentally, the naming of the variable in the question's example is the singular 'letter', which might imply that it represents only a single letter; the example code makes it clear that its a set of possible letters and that multiple values are allowed, so consider renaming the variable 'letters'.

How about

if ((letter & Letters.AB) > 0) 

?

I created a simple extension method that does not need a check on Enum types:

public static bool HasAnyFlag(this Enum value, Enum flags) { return value != null && ((Convert.ToInt32(value) & Convert.ToInt32(flags)) != 0); } 

It also works on nullable enums. The standard HasFlag method does not, so I created an extension to cover that too.

public static bool HasFlag(this Enum value, Enum flags) { int f = Convert.ToInt32(flags); return value != null && ((Convert.ToInt32(value) & f) == f); } 

A simple test:

[Flags] enum Option { None = 0x00, One = 0x01, Two = 0x02, Three = One | Two, Four = 0x04 } [TestMethod] public void HasAnyFlag() { Option o1 = Option.One; Assert.AreEqual(true, o1.HasAnyFlag(Option.Three)); Assert.AreEqual(false, o1.HasFlag(Option.Three)); o1 |= Option.Two; Assert.AreEqual(true, o1.HasAnyFlag(Option.Three)); Assert.AreEqual(true, o1.HasFlag(Option.Three)); } [TestMethod] public void HasAnyFlag_NullableEnum() { Option? o1 = Option.One; Assert.AreEqual(true, o1.HasAnyFlag(Option.Three)); Assert.AreEqual(false, o1.HasFlag(Option.Three)); o1 |= Option.Two; Assert.AreEqual(true, o1.HasAnyFlag(Option.Three)); Assert.AreEqual(true, o1.HasFlag(Option.Three)); } 

Enjoy!

There are a lot of answers on here but I think the most idiomatic way to do this with Flags would be Letters.AB.HasFlag(letter) or (Letters.A | Letters.B).HasFlag(letter) if you didn't already have Letters.AB. letter.HasFlag(Letters.AB) only works if it has both.

You can use this extension method on enum, for any type of enums:

public static bool IsSingle(this Enum value) { var items = Enum.GetValues(value.GetType()); var counter = 0; foreach (var item in items) { if (value.HasFlag((Enum)item)) { counter++; } if (counter > 1) { return false; } } return true; } 

Starting with .Net 4, you can use a shorthand version without explicitly specifying &:

if(Letters.AB.HasFlag(Letters.C)) 

Would this work for you?

if ((letter & (Letters.A | Letters.B)) != 0) 

if((int)letter != 0) { } 

You could just check if the value is not zero.

if ((Int32)(letter & Letters.AB) != 0) { } 

But I would consider it a better solution to introduce a new enumeration value with value zero and compare agains this enumeration value (if possible because you must be able to modify the enumeration).

[Flags] enum Letters { None = 0, A = 1, B = 2, C = 4, AB = A | B, All = AB | C } if (letter != Letters.None) { } 

UPDATE

Missread the question - fixed the first suggestion and just ignore the second suggestion.

There are two aproaches that I can see that would work for checking for any bit being set.

Aproach A

if (letter != 0) { } 

This works as long as you don't mind checking for all bits, including non-defined ones too!

Aproach B

if ((letter & Letters.All) != 0) { } 

This only checks the defined bits, as long as Letters.All represents all of the possible bits.

For specific bits (one or more set), use Aproach B replacing Letters.All with the bits that you want to check for (see below).

if ((letter & Letters.AB) != 0) { } 

Can we find out easily and efficiently whether at least one flag is set?

Well, if you are satisfied with checking whether at least one flag bit is set, then yes!

Usage:

if (EnumHelper.HasAnyFlagBitsSet(letter)) 

Implementation:

public static class EnumHelper { static EnumHelper() { // Required to get correct behavior in GetNumericValue // Because we will overlap the enum type with a ulong, left-aligned if (!BitConverter.IsLittleEndian) throw new NotSupportedException("This type is only supported on little-endian architectures."); } /// <summary> /// <para> /// Returns whether the given enum value has any bits set that occurs in a defined flag for <typeparamref name="T"/>. /// </para> /// <para> /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>. /// </para> /// </summary> public static bool HasAnyFlagBitsSet<T>(T enumValue) where T : unmanaged, Enum { var numericValue = GetNumericValue(enumValue); // Take the value that has all the permitted bits set // Use & to keep only the corresponding bits from the input value // Check that the input value provided at least one such bit return (numericValue & FlagValueCache<T>.AllFlagsSetValue) != 0; } /// <summary> /// <para> /// Returns whether the given enum value has any bits set that are set in <paramref name="flags"/>. /// </para> /// <para> /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>. /// </para> /// </summary> public static bool HasAnyFlagBitsSet<T>(T enumValue, T flags) where T : unmanaged, Enum { var numericValue = GetNumericValue(enumValue); var numericFlags = GetNumericValue(flags); // Use & to keep only the bits present in flags // Check that the input value provided at least one such bit return (numericValue & flags) != 0; } // Actually, have a bonus method as well, since this is a common operation: /// <summary> /// <para> /// Returns whether the given enum value consists exclusively of defined flags for <typeparamref name="T"/>. /// The result is false if a bit is set that is not part of any value defined by <typeparamref name="T"/>. /// </para> /// <para> /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>. /// </para> /// </summary> public static bool HasDefinedFlags<T>(T enumValue) where T : unmanaged, Enum { var numericValue = GetNumericValue(enumValue); // Take the value that has all the permitted bits set // Use ~ to get a value with all the forbidden bits set // Use & to keep only the corresponding bits from the input value // Check that the input value provided no such forbidden bits return (numericValue & ~FlagValueCache<T>.AllFlagsSetValue) == 0; } /// <summary> /// <para> /// Returns the numeric value of the given <paramref name="enumValue"/>. /// </para> /// <para> /// The resulting <see cref="ulong"/> can be cast to the intended integral type, even if it is a signed type. /// </para> /// </summary> [MethodImpl(MethodImplOptions.AggressiveInlining)] public static ulong GetNumericValue<T>(T enumValue) where T : unmanaged, Enum { Span<ulong> ulongSpan = stackalloc ulong[] { 0UL }; Span<T> span = MemoryMarshal.Cast<ulong, T>(ulongSpan); span[0] = enumValue; return ulongSpan[0]; } /// <summary> /// Statically caches a "full" flags value each enum type for which this class is accessed. /// </summary> internal static class FlagValueCache<T> where T : unmanaged, Enum { /// <summary> /// Each bit that is set in any of the type's defined values is also set in this value. /// </summary> public static ulong AllFlagsSetValue { get; } static FlagValueCache() { if (typeof(T).BaseType != typeof(Enum)) throw new Exception("The type parameter must be an enum type."); foreach (var value in (T[])Enum.GetValues(typeof(T))) AllFlagsSetValue |= GetNumericValue(value); } } } 

What does it mean that we are checking if at least one flag bit is set?

Well, this solution may fail to answer correctly for nonsensical enums like the following:

[Flags] public enum Nonsense { One = 1, // Eh, why does this value need TWO bits when those bits are NOT defined as individual values? TwoAndFour = 2 | 4, } 

Here, EnumHelper.HasAnyFlagBitSet((Nonsense)2) would return true, which is technically incorrect, since 2 is not a defined flag.

However, it works perfectly fine for all sensible flags enums, including ones with multi-flags:

[Flags] public enum Fine { One = 1, Two = 2, Four = 4, // Fine, and sensible, since these flags exist individually TwoAndFour = 2 | 4, } 

You can use the bitwise AND operator (&) directly on the combined flag constant and check if the result is not equal to zero.

Here's an example using the AB flag from your Letters enum:

if ((letter & Letters.AB) != 0) { // AB flag is set } 

This works because the bitwise AND operation will only produce a non-zero result if at least one of the flags in Letters. AB is set in the letter variable. If the result is zero, it means none of the flags in Letters. AB are set in letter.

You can apply the same approach to check for any other combined flag constant, such as All:

if ((letter & Letters.All) != 0) { // At least one flag from All is set } 

By using the bitwise AND operator in this way, you can simplify the check and avoid explicitly comparing against the flag constant itself.