What is the default value for enum variable?

An enum variable, anyone know if it is always defaulting to the first element?

3 Answers

It is whatever member of the enumeration represents the value 0. Specifically, from the documentation:

The default value of an enum E is the value produced by the expression (E)0.

As an example, take the following enum:

enum E { Foo, Bar, Baz, Quux } 

Without overriding the default values, printing default(E) returns Foo since it's the first-occurring element.

However, it is not always the case that 0 of an enum is represented by the first member. For example, if you do this:

enum F { // Give each element a custom value Foo = 1, Bar = 2, Baz = 3, Quux = 0 } 

Printing default(F) will give you Quux, not Foo.

If none of the elements in an enum G correspond to 0:

enum G { Foo = 1, Bar = 2, Baz = 3, Quux = 4 } 

default(G) returns literally 0, although its type remains as G (as quoted by the docs above, a cast to the given enum type).

I think it's quite dangerous to rely on the order of the values in a enum and to assume that the first is always the default. This would be good practice if you are concerned about protecting the default value.

enum E { Foo = 0, Bar, Baz, Quux } 

Otherwise, all it takes is a careless refactor of the order and you've got a completely different default.

You can use this snippet :-D

using System; using System.Reflection; public static class EnumUtils { public static T GetDefaultValue<T>() where T : struct, Enum { return (T)GetDefaultValue(typeof(T)); } public static object GetDefaultValue(Type enumType) { var attribute = enumType.GetCustomAttribute<DefaultValueAttribute>(inherit: false); if (attribute != null) return attribute.Value; var innerType = enumType.GetEnumUnderlyingType(); var zero = Activator.CreateInstance(innerType); if (enumType.IsEnumDefined(zero)) return zero; var values = enumType.GetEnumValues(); return values.GetValue(0); } } 

Example:

using System; public enum Enum1 { Foo, Bar, Baz, Quux } public enum Enum2 { Foo = 1, Bar = 2, Baz = 3, Quux = 0 } public enum Enum3 { Foo = 1, Bar = 2, Baz = 3, Quux = 4 } [DefaultValue(Enum4.Bar)] public enum Enum4 { Foo = 1, Bar = 2, Baz = 3, Quux = 4 } public static class Program { public static void Main() { var defaultValue1 = EnumUtils.GetDefaultValue<Enum1>(); Console.WriteLine(defaultValue1); // Foo var defaultValue2 = EnumUtils.GetDefaultValue<Enum2>(); Console.WriteLine(defaultValue2); // Quux var defaultValue3 = EnumUtils.GetDefaultValue<Enum3>(); Console.WriteLine(defaultValue3); // Foo var defaultValue4 = EnumUtils.GetDefaultValue<Enum4>(); Console.WriteLine(defaultValue4); // Bar } }