(C++) Using '::' to get enum members?
Author
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?
The :: is the scope resolution operator. Use it like:
or, like thie:
Skizz
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
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
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
You're correct. The way to overcome this is to put the enum in a class/struct or use a namespace, e.g.
struct Result
{
enum types {Right, Wrong};
};
However, now when you want to pass the enum in as an argument, you need to type the struct name first, here's a silly example:
HTH
struct Result
{
enum types {Right, Wrong};
};
However, now when you want to pass the enum in as an argument, you need to type the struct name first, here's a silly example:
struct Result{ enum types {Right, Wrong};};void MyFunction(Result::types result){ if (result == Result::Right) { std::cout << "You were right!" << std::endl; } else { assert(result == Result::Wrong); //Shouldn't happen unless we added more types to the enum and forgot to update this peice of code! std::cout << "You were wrong :(" << std::endl; }}HTH
Also note that in C++/cli the above code would have to be something like
if(res == Result::types::Right) {}
Full qualification of the enum member is needed. So Deckards, your first example would be the prefered solution with c++/cli. Just in case.
if(res == Result::types::Right) {}
Full qualification of the enum member is needed. So Deckards, your first example would be the prefered solution with c++/cli. Just in case.
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.
Wait a minute, can't you just do this:
Abeit unsafe I know due to collisions, but it compiled for me?
- Drew
// 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
Author
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,
};
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,
};
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):
Used something like this:
#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.#endifUsed something like this:
#include "nsenum.hpp"NSENUM_BEGIN(stuff) alpha, beta, gammaNSENUM_END(stuff) This topic is closed to new replies.
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