| title | enum (C# Reference) | ||
|---|---|---|---|
| ms.date | 07/20/2015 | ||
| ms.prod | .net | ||
| ms.technology |
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| ms.topic | article | ||
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| ms.assetid | bbeb9a0f-e9b3-41ab-b0a6-c41b1a08974c | ||
| caps.latest.revision | 36 | ||
| author | BillWagner | ||
| ms.author | wiwagn |
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 Day {Sat, Sun, Mon, Tue, Wed, Thu, Fri};
Enumerators can use initializers to override the default values, as shown in the following example.
enum Day {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.
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 Day : 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 Day 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.
Note
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)Day.Sun;
When you apply xref:System.FlagsAttribute?displayProperty=nameWithType 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 xref:System.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.
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, Day, is declared. Two enumerators are explicitly converted to integer and assigned to integer variables.
[!code-csharpcsrefKeywordsTypes#10]
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.
[!code-csharpcsrefKeywordsTypes#11]
The following code example illustrates the use and effect of the xref:System.FlagsAttribute?displayProperty=nameWithType attribute on an enum declaration.
[!code-csharpcsrefKeywordsTypes#12]
If you remove Flags, the example displays the following values:
5
5
[!INCLUDECSharplangspec]
C# Reference
Enumeration Types
C# Keywords
Integral Types Table
Built-In Types Table
Implicit Numeric Conversions Table
Explicit Numeric Conversions Table
Enum Naming Conventions