(C++) Using '::' to get enum members?
February 06, 2005 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?
The Sands of Time Are Running Low
794
February 06, 2005 11:50 AM
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
11,263
February 06, 2005 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
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
February 06, 2005 11:52 AM
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
February 06, 2005 01:51 PM
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.
1,658
February 06, 2005 01:58 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.
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan
1,865
February 06, 2005 02:29 PM
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
February 06, 2005 03:32 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,
};
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,
};
The Sands of Time Are Running Low
1,088
February 06, 2005 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):
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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