Enum C# vs C++

In C# this is perfectly legal :

enum A
{
    None,
    Value1,
    Value2
}

enum B
{
    None,
    Sometype1,
    Sometype2
}

C++ complain that None is already define, so is it possible to accomplish the same thing in C++ ?

Thanks

No.  According to the C standard, identifiers in an enumerator list must be distinct from all other identifiers declared in the same scope.

EDIT:  After reading the C++ standard, it should seem that I'm wrong   If you declare your enum as enum class, you should be able to reuse names.  So it would look like this:

enum class A
{
    None,
    Value1,
    Value2
}

enum class B
{
    None,
    Sometype1,
    Sometype2
}

//... where you're using these enums

B someVariable = B::None;
B someOtherVariable = B::Value1;
A yetAnotherVariable = A::None;

CannotResolveSymbol said:

No.  According to the C standard, identifiers in an enumerator list must be distinct from all other identifiers declared in the same scope.

EDIT:  After reading the C++ standard, it should seem that I'm wrong   If you declare your enum as enum class, you should be able to reuse names.  So it would look like this:

enum class A
{
    None,
    Value1,
    Value2
}

enum class B
{
    None,
    Sometype1,
    Sometype2
}

//... where you're using these enums

B someVariable = B::None;
B someOtherVariable = B::Value1;
A yetAnotherVariable = A::None;

Downsides:  you have to use A:: or B:: to access the enum's values and you can't treat your enumeration's values as an int or bool anymore (so int number = A::None and A enumValue = 1 will not work).

EDIT2:  enum class doesn't seem to be in the C++ 1998 standard...  your mileage may vary (it may or may not be implemented in Visual Studio; can't try right now).  Guess I should be more careful which document I pull up (I grabbed the Oct. 2008 draft of the C++ standard).  If it's not in VS, your best bet is to prefix your constants with some distinct prefix (like ANone and BNone).

Sven Groot said:

CannotResolveSymbol said:

*snip*

enum class is a construct of C++/CLI, it defines a managed enum type. It is not available in regular C++.

I don't believe there is a way to do what you want using standard C++. At least not in C++98 or C99.

CannotResolveSymbol said:

Sven Groot said:

*snip*

enum class is planned for C++ 0x; when I pulled up the C++ standard, I grabbed the latest draft instead of the current version...  my mistake.

Maybe I can go with something like this until C++ 0x is release and implemented in gcc and VC compiler ?

class A
{
public:
    enum Value { None, Value1, Value2 };
};

class B
{
public:
    enum Value { None, SomeType1, SomeType2 };
};

int main()
{
    A::Value a = A::None;
    B::Value b = B::None;
}

cro said:

Maybe I can go with something like this until C++ 0x is release and implemented in gcc and VC compiler ?

class A
{
public:
    enum Value { None, Value1, Value2 };
};

class B
{
public:
    enum Value { None, SomeType1, SomeType2 };
};

int main()
{
    A::Value a = A::None;
    B::Value b = B::None;
}

That'd work. With some trickery you would be able to declare variables without using the ::Value bit too, like this:

class MyEnum
{
public:
    enum Value
    {
        None,
        Value1,
        Value2
    };

    MyEnum(Value value) : _value(value) { }

    operator Value() const
    {
        return _value;
    }
private:
    Value _value;
};

MyEnum x = MyEnum::Value1;

Sven Groot said:

cro said:

*snip*

That'd work. With some trickery you would be able to declare variables without using the ::Value bit too, like this:

class MyEnum
{
public:
    enum Value
    {
        None,
        Value1,
        Value2
    };

    MyEnum(Value value) : _value(value) { }

    operator Value() const
    {
        return _value;
    }
private:
    Value _value;
};

Then you could simply use it as:

MyEnum x = MyEnum::Value1;

You'd have to repeat that code for every enum though.

Thanks !

OR, you could try using namespaces:

namespace A {
	enum AA{ None, Value1, Value2 };
}

namespace B {
	enum BB { None, Sometype1, Sometype2 };
}

...
...
	int a   = A::None;
	int aa  = A::AA::None;
	int b   = B::None;
	int bb  = B::BB::None;