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enum (C# Reference)

The enum keyword is used to declare an enumeration, a distinct type that consists of a set of named constants called the enumerator list.

Usually it is best to define an enum directly within a namespace so that all classes in the namespace can access it with equal convenience. However, an enum can also be nested within a class or struct.

By default, the first enumerator has the value 0, and the value of each successive enumerator is increased by 1. For example, in the following enumeration, Sat is 0, Sun is 1, Mon is 2, and so forth.

enum Days {Sat, Sun, Mon, Tue, Wed, Thu, Fri};

Enumerators can use initializers to override the default values, as shown in the following example.

enum Days {Sat=1, Sun, Mon, Tue, Wed, Thu, Fri};

In this enumeration, the sequence of elements is forced to start from 1 instead of 0. However, including a constant that has the value of 0 is recommended. For more information, see Enumeration Types (C# Programming Guide).

Every enumeration type has an underlying type, which can be any integral type except char. The default underlying type of enumeration elements is int. To declare an enum of another integral type, such as byte, use a colon after the identifier followed by the type, as shown in the following example.

enum Days : byte {Sat=1, Sun, Mon, Tue, Wed, Thu, Fri};

The approved types for an enum are byte, sbyte, short, ushort, int, uint, long, or ulong.

A variable of type Days can be assigned any value in the range of the underlying type; the values are not limited to the named constants.

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

NoteNote

An enumerator cannot contain white space in its name.

The underlying type specifies how much storage is allocated for each enumerator. However, an explicit cast is necessary to convert from enum type to an integral type. For example, the following statement assigns the enumerator Sun to a variable of the type int by using a cast to convert from enum to int.

int x = (int)Days.Sun;

When you apply System.FlagsAttribute to an enumeration that contains elements that can be combined with a bitwise OR operation, the attribute affects the behavior of the enum when it is used with some tools. You can notice these changes when you use tools such as the Console class methods and the Expression Evaluator. (See the third example.)

Just as with any constant, all references to the individual values of an enum are converted to numeric literals at compile time. This can create potential versioning issues as described in Constants (C# Programming Guide).

Assigning additional values to new versions of enums, or changing the values of the enum members in a new version, can cause problems for dependent source code. Enum values often are used in switch statements. If additional elements have been added to the enum type, the default section of the switch statement can be selected unexpectedly.

If other developers use your code, you should provide guidelines about how their code should react if new elements are added to any enum types.

In the following example, an enumeration, Days, is declared. Two enumerators are explicitly converted to integer and assigned to integer variables.


public class EnumTest
{
    enum Days { Sun, Mon, Tue, Wed, Thu, Fri, Sat };

    static void Main()
    {
        int x = (int)Days.Sun;
        int y = (int)Days.Fri;
        Console.WriteLine("Sun = {0}", x);
        Console.WriteLine("Fri = {0}", y);
    }
}
/* Output:
   Sun = 0
   Fri = 5
*/

In the following example, the base-type option is used to declare an enum whose members are of type long. Notice that even though the underlying type of the enumeration is long, the enumeration members still must be explicitly converted to type long by using a cast.

public class EnumTest2
{
    enum Range : long { Max = 2147483648L, Min = 255L };
    static void Main()
    {
        long x = (long)Range.Max;
        long y = (long)Range.Min;
        Console.WriteLine("Max = {0}", x);
        Console.WriteLine("Min = {0}", y);
    }
}
/* Output:
   Max = 2147483648
   Min = 255
*/

The following code example illustrates the use and effect of the System.FlagsAttribute attribute on an enum declaration.

// Add the attribute Flags or FlagsAttribute.
[Flags]
public enum CarOptions
{
    // The flag for SunRoof is 0001.
    SunRoof = 0x01,
    // The flag for Spoiler is 0010.
    Spoiler = 0x02,
    // The flag for FogLights is 0100.
    FogLights = 0x04,
    // The flag for TintedWindows is 1000.
    TintedWindows = 0x08,
}

class FlagTest
{
    static void Main()
    {
        // The bitwise OR of 0001 and 0100 is 0101.
        CarOptions options = CarOptions.SunRoof | CarOptions.FogLights;

        // Because the Flags attribute is specified, Console.WriteLine displays 
        // the name of each enum element that corresponds to a flag that has 
        // the value 1 in variable options.
        Console.WriteLine(options);
        // The integer value of 0101 is 5.
        Console.WriteLine((int)options);
    }
}
/* Output:
   SunRoof, FogLights
   5
*/

If you remove Flags, the example displays the following values:

5

5

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

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