Accessing to enum values by '::' in C++

Question

I have class like following:

class Car 
{ 
public: 
 Car(); 
 // Some functions and members and <b>enums</b> 
 enum Color
 {
 Red,
 Blue,
 Black
 }; 
 Color getColor();
 void setColor(Color); 
private: 
 Color myColor;
}

I want to:

1. access to Color values as Color::Red. It is really hardly to understand code when Car::Red is used, when class have a lot enums, subclasses etc.
2. use type Color as function argument or return value
3. use variable type Color in switch

I know 3 partial solutions:

1. Using embedded class Color and enum in it
2. Using embedded namespace Color and enum in it
3. Using enum class

1 and 2 solutions solves a Color::Red accession problem, but I can't use functions like Color getColor() and void setColor(Color).

3 solution has a problem: VS2010 doen't support enum class. GCC v.4.1.2 doesn't support it too. I don't know about later versions of gcc.

Yes, I'm working on cross-platform project.
I have found this solution, but it seems ... heavy.
I hope somebody can help me here :)

• leftaroundabout: GCC 4.6 (with -std=c++0x) supports enum class, and also allows Color::Red for regular enums.
• CharlesB: side note, please indent code with 4 spaces instead of using pre/code tags
• Jury: I found than VS2010 has partially support of Strongly typed enums.

Answer 1

In current C++ (i.e. C++11 and beyond), you can already access enum values like that:

enum Color { Red };
Color c = Color::Red;
Color d = Red;

You can go further and enforce the use of this notation:

enum class Color { Red };
Color c = Color::Red;
// Color d = Red; <-- error now

And on a sidenote, you now define the underlying type, which was previously only possible with hacky code (FORCEDWORD or so anyone?):

enum class Color : char { Red };

• Jury: You are right, but there is no compilers with full support C++11 features. Yes, GCC 4.6 and 4.7 supports it, but my project must be compiled for Windows too. VS2010 doesn't supports it. May be you know the some patch for it?
• Sebastian Mach: You can try MinGW, which is the windows port of GCC. MSVC is closed source and there are no patches.
• Cătălina Sîrbu: // Color d = Red; <-- error now is not giving any error at the moment. Also I can acces the values from the enum declared as a global one by typing their names (e.g cout << Red << endl;)
• Sebastian Mach: @CătălinaSîrbu: Did you declare it as enum class or just enum?
• Cătălina Sîrbu: I declared them just enum

Answer 2

Name the enum inside the nested class (as example one):

class Car
{
public:
 struct Color
 {
 enum Type
 {
 Red,
 Blue,
 Black
 };
 };
 Color::Type getColor();
 void setColor(Color::Type);
};

• iammilind: You can also mention about C++11 feature enum class.
• Jury: And use getter and setter of Color in getter and setter of Car?
• Konrad: The Color:: part is not needed here?
• Mark B: @Konrad Woops, fixed my example so now it's needed (since Color is intended to be a nested class).
• Mark B: @iammilind The OP doesn't want to use enum class because it's not uniformly supported across all needed platforms.

Answer 3

When I want to do something like this I tend to use a namespace and a typedef outside of th namespace (though usually I'm doing this globally rather than inside a class). Something like this:

namespace colors 
{
 enum Color 
 {
 Red,
 Blue
 ...
 }
}
typedef colors::Color Color;

This way you use the namespace to get at the actual colors, but the Color type itself is still globally accessible:

Color myFav = colors::Red;

• Jury: VS2010 : error C2059: syntax error : 'namespace' | GCC 4.1.2 : error: expected unqualified-id before 'namespace'
• obmarg: @Jury Probably because you're not allowed to declare namespaces inside classes. Like I said, I usually do this globally. You can always use a nested class if you really want to keep it within a class - the principle's the same.
• Alex: The typedef isn't really necessary, and I would just put Color as the namespace name and not give the enum a name. I use the namespace method all the time since it's so elegant. Here's some more information about using enums: inphamousdevelopment.wordpress.com/2012/04/02/…
• obmarg: @alex The typedef isn't neccesary, but it's a lot nicer to have a typedef than it is to type colors::Color every time you want to store an enum value somewhere. As for not giving the enum a name - what if you want to use the enum type later on? I guess you're maybe implying you should just use an int, but why throw away type information (and therefore type-safety) like that?
• obmarg: @alex I'd consider that very bad practice. Firstly, you're throwing type safety out the window: normally your compiler could warn you if you try to use a non-Color in place of a Color - but not if you just use an int. Secondly, it just makes things harder to understand for anyone reading the code - how is anyone meant to know at a glance that the function actually accepts values of the Color enum, rather than just any integer from 0 - 65536? Since there's no type safety, anyone could misunderstand the parameter, pass in a value that makes no sense and things would compile fine.