enum class (C++ Component Extensions)
The latest version of this topic can be found at enum class (C++ Component Extensions).
Declares an enumeration at namespace scope, which is a user-defined type consisting of a set of named constants called enumerators.
All Runtimes
Remarks
C++/CX and C++/CLI support public enum class and private enum class which are similar to the standard C++ enum class but with the addition of the accessibility specifier. Under /clr, the C++11 enum class type is permitted but will generate warning C4472 which is intended to ensure that you really want the ISO enum type and not the C++/CX and C++/CLI type. For more information about the ISO Standard C++ enum keyword, see Enumerations.
Windows Runtime
Syntax
access
enum class
enumeration-identifier
[:underlying-type] { enumerator-list } [var];
accessenum structenumeration-identifier[:underlying-type] { enumerator-list } [var];
Parameters
access
The accessibility of the enumeration, which can be public or private.
enumeration-identifier
The name of the enumeration.
underlying-type
(Optional) The underlying type of the enumeration.
(Optional. Windows Runtime only) The underlying type of the enumeration, which can be bool, char, char16, int16, uint16, int, uint32, int64, or uint64.
enumerator-list
A comma-delimited list of enumerator names.
The value of each enumerator is a constant expression that is either defined implicitly by the compiler, or explicitly by the notation, enumerator=constant-expression. By default, the value of the first enumerator is zero if it is implicitly defined. The value of each subsequent implicitly-defined enumerator is the value of the previous enumerator + 1.
var
(Optional) The name of a variable of the enumeration type.
Remarks
For more information, and examples, see Enums.
Note that the compiler emits error messages if the constant expression that defines the value of an enumerator cannot be represented by the underlying-type. However, the compiler does not report an error for a value that is inappropriate for the underlying type. For example:
If underlying-type is numeric, and an enumerator specifies the maximum value for that type, the value of the next implicitly defined enumeratoin cannot be represented.
If underlying-type is
bool, and more than two enumerators are implicitly defined, the enumerators after the first two cannot be represented.If underlying-type is
char16, and the enumeration value ranges from 0xD800 through 0xDFFF, the value can be represented. However, the value logically incorrect because it represents half a Unicode surrogate pair and should not appear in isolation.
Requirements
Compiler option: /ZW
Common Language Runtime
Syntax
access
enum class
name [:type] { enumerator-list } var;
accessenum structname [:type] { enumerator-list } var;
Parameters
access
The accessibility of the enum. Can be either public or private.
enumerator-list
A comma-separated list of the identifiers (enumerators) in the enumeration.
name
The name of the enumeration. Anonymous managed enumerations are not allowed.
type (optional)
The underlying type of the identifiers. This can be any scalar type, such as signed or unsigned versions of int, short, or long. bool or char is also allowed.
var (optional)
The name of a variable of the enumeration type.
Remarks
enum class and enum struct are equivalent declarations.
There are two types of enums: managed or C++/CX and standard.
A managed or C++/CX enum might be defined as follows,
public enum class day {sun, mon };
and is semantically equivalent to:
ref class day {
public:
static const int sun = 0;
static const int mon = 1;
};
A standard enum might be defined as follows:
enum day2 { sun, mon };
and is semantically equivalent to:
static const int sun = 0;
static const int mon = 1;
Managed enumerator names (identifiers) are not injected into the scope where the enumeration is defined; all references to the enumerators must be fully qualified (name::identifier). For this reason, you cannot define an anonymous managed enum.
The enumerators of a standard enum are strongly injected into the enclosing scope. That is, if there is another symbol with the same name as an enumerator in the enclosing scope, the compiler will generate an error.
In Visual C++ 2002 and Visual C++ 2003, enumerators were weakly injected (visible in the enclosing scope unless there was another identifier with the same name).
If a standard C++ enum is defined (without class or struct), compiling with /clr will cause the enumeration to be compiled as a managed enum. The enumeration still has the semantics of an unmanaged enumeration. Note, the compiler injects an attribute, Microsoft::VisualC::NativeEnumAttribute, which the Visual C++ compiler recognizes, to identify a programmer's intent for the enum to be a native enum. Other compilers will simply see the standard enum as a managed enum.
A named, standard enum compiled with /clr will be visible in the assembly as a managed enum, and can be consumed by any other managed compiler. However, an unnamed standard enum will not be publicly visible from the assembly.
In Visual C++ 2002 and Visual C++ 2003, a standard enum used as the type in a function parameter:
// mcppv2_enum.cpp
// compile with: /clr
enum E { a, b };
void f(E) {System::Console::WriteLine("hi");}
int main() {
E myi = b;
f(myi);
}
would emit the following in MSIL for the function signature:
void f(int32);
However, in current versions of the compiler, the standard enum is emitted as a managed enum with a [NativeEnumAttribute] and the following in MSIL for the function signature:
void f
(E)
For more information about native enums, see C++ Enumeration Declarations.
For more information on CLR enums, see:
Requirements
Compiler option: /clr
Examples
Example
desc
// mcppv2_enum_2.cpp
// compile with: /clr
// managed enum
public enum class m { a, b };
// standard enum
public enum n { c, d };
// unnamed, standard enum
public enum { e, f } o;
int main()
{
// consume managed enum
m mym = m::b;
System::Console::WriteLine("no automatic conversion to int: {0}", mym);
System::Console::WriteLine("convert to int: {0}", (int)mym);
// consume standard enum
n myn = d;
System::Console::WriteLine(myn);
// consume standard, unnamed enum
o = f;
System::Console::WriteLine(o);
}
Output
no automatic conversion to int: b
convert to int: 1
1
1