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(C++) Using '::' to get enum members?

Started by Deckards Feb 6, 2005 at 11:32 AM 8 replies 16k views

Original Post

Feb 6, 2005 at 11:32 AM

In C++, we can't use '::' to get enum members, am I right? With the following declaration: enum Result { Right, Wrong, }; We can't do this: Result res = Result::Right; Is there a way to overcome this?

Skizz

Feb 6, 2005 at 11:50 AM

The :: is the scope resolution operator. Use it like:

class Result{public:  typedef enum an_enum  {    Right,    Wrong  } AnEnum;};Result::AnEnum a = Result::Right;

or, like thie:

// in a headernamespace Result;typedef enum an_enum  {    Right,    Wrong  } AnEnum;// in sourceResult::AnEnum a = Result::Right;// orusing namespace Result;AnEnum a = Right;

Skizz

_the_phantom_

Feb 6, 2005 at 11:51 AM

Result is a type, not a namespace/scope.
I wanted todo the same thing a while back, so I wrapped the values in a namespace and then typedef'd the type so I could refer to it for parameter reasons

edit: yeah, what Skizz said

desertcube

Feb 6, 2005 at 11:54 AM

OK, the AP was me + beaten by skizz + _the_phantom_

Fruny

Feb 6, 2005 at 1:58 PM

Quote:
Original post by Deckards
Is there a way to overcome this?

Unlikes class types (struct, class, union), enumerations do not create a scope. Use a namespace or a class type wrapper.

Drew_Benton

Feb 6, 2005 at 2:29 PM

Wait a minute, can't you just do this:

// somefile.henum Result{    Right,    Wrong,};// somefile.cpp...void Function(){   Result res = Right;}

Abeit unsafe I know due to collisions, but it compiled for me?

- Drew

Deckards

Feb 6, 2005 at 3:32 PM

Thanks for your answers.

Nesting the enum in another type resolves the readability problem but we still have to use "Result::types" which is not very nice.

I think I'll stick witch the following approach:
enum Result
{
Result_Right,
Result_Wrong,
};

Null and Void

Feb 6, 2005 at 10:55 PM

I cheat, here's a simplified version of what I use (ignore the seperate operator and constructor macros, they're just part of my more customizable solution that I'm being lazy about and not removing):

#ifndef INC_NSENUM_HPP#define INC_NSENUM_HPP#define NSENUM_OPERATORS(enum_name)                         \ 	inline operator internal_type() const {             \ 		return m_value;                             \ 	}                                                   \ 	                                                    \ 	inline bool operator==(internal_type value) const { \ 		return m_value == value;                    \ 	}                                                   \ 	inline bool operator!=(internal_type value) const { \ 		return m_value != value;                    \ 	}#define NSENUM_CONSTRUCTORS(enum_name)                           \ 	inline enum_name() {                                     \ 	}                                                        \ 	inline enum_name(internal_type value) : m_value(value) { \ 	}#define NSENUM_BEGIN(enum_name)      \ class enum_name {                    \ 	public:                      \ 		enum internal_type {#define NSENUM_END(enum_name)                  \ 		};                             \ 	private:                               \ 		internal_type m_value;         \ 	public:                                \ 		NSENUM_OPERATORS(enum_name)    \ 		NSENUM_CONSTRUCTORS(enum_name) \ };// If you copy/paste this, remove the spaces after the// backslashes. They're just there to make the forums happy.#endif

Used something like this:

#include "nsenum.hpp"NSENUM_BEGIN(stuff)	alpha,	beta,	gammaNSENUM_END(stuff)

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