Enum inside enum on C++

Question

I am trying to get working a structure based on constants. I have ObjectTypes (KEYBOARD, MOUSE, HAPTIC...) which can have InputTypes (the MOUSE can be DEFAULT and INVERSE, while KEYBOARD can be DEFAULT and NUMERIC and HAPTIC only can be DEFAULT).

To get this working I'm trying to use enums inside enums in a class called Constants in C++. It might work passing a ObjectTypes parameter and a InputTypes parameter to a function, so I need something like this in the prototype:

changeInputSystem(SimulatorConstants::InputObject input, SimulatorConstants::InputTypes type)

But in C++, when I declare an enum every value taken out from this (internally) and some of them replace the others.

My code right now (and not working) is:

    enum InputObject {
        KEYBOARD,
    MOUSE,
    HAPTIC
};

enum InputTypes {
    enum KeyboardTypes {
        DEFAULT
    };
    enum MouseTypes {
        DEFAULT,
        INVERSE
    };
    enum HapticTypes {
        DEFAULT
    };
};

NOTE: I know there is no inheritance between enums, so I need any solution that can work in a similar way. Thanks.

You can't have nested enums. Enums are named constants and not a user-defined data type like struct or classes. — Arun, Apr 11 '13 at 13:32
As I said I kwnow this, but don't know how to solve it with another structure — droidpl, Apr 11 '13 at 13:33
Why not have struct InputTypes { enum { ... } enum {..} } instead? — Arun, Apr 11 '13 at 13:35
I'll try it. What about `enum class` structure? It's new on C++11 — droidpl, Apr 11 '13 at 13:37
`enum class` is actually a _scoped enum_. You cannot nest types in there, too. — dyp, Apr 11 '13 at 13:38
If you can use `enum class` that will solve you the conflicts of several `DEFAULT`s. You'd still need to put the type enum classes inside a struct or a namespace to bundle them. — StoryTeller - Unslander Monica, Apr 11 '13 at 13:38
Ok, I'm using VS2010 so don't have enum class as I see. How to solve the defaults then? I want to use it on a switch statement — droidpl, Apr 11 '13 at 13:44
@feantury See ["enum class" emulation or solid alternative for MSVC 10.0](http://stackoverflow.com/questions/4980280/enum-class-emulation-or-solid-alternative-for-msvc-10-0) — Bo Persson, Apr 11 '13 at 14:01
Oh my god! What a trick! Finally I've found another answer that looks easier and reduce conmplexity — droidpl, Apr 11 '13 at 14:22

score 1 · Answer 1 · answered Apr 11 '13 at 14:04

1

It works if you do the whole thing object-oriented. So instead of having enums for everything just have classes:

class InputObject {};

class Mouse : public InputObject
{
  void setDefault();
  void setInverse();
};

This way the type of the InputObject can be saved inside the object and you only pass around the actual InputObject.

answered Apr 11 '13 at 14:04

littleimp

1,159
9
13

Yes, it works, but I can't do what I want with a switch statement, making my code cleaner – droidpl Apr 11 '13 at 14:14
@Feantury You can use method _inheritance_ instead of a _switch_. – Sulthan Apr 11 '13 at 14:26
For me it's a valid answer, but too complex only to manage some constants, I prefere enums, struct and overload. Thanks anyway – droidpl Apr 11 '13 at 14:30

score 1 · Answer 2 · answered Apr 24 '14 at 13:18

Like written in the comments, if you have access to a C++11 compiler, better to use an enum class, which would change your own accepted answer (at the time of this writing) code into:

enum class KeyboardTypes {
   DEFAULT
};
enum class MouseTypes {
  DEFAULT,
   INVERSE
};
enum class HapticTypes {
   DEFAULT
};

And of course, your overloaded functions can be changed into a more natural version:

void changeInputSystem(SimulatorConstants::MouseTypes type);
void changeInputSystem(SimulatorConstants::KeyboardTypes type);
void changeInputSystem(SimulatorConstants::HapticTypes type);

And, as a bonus, there will be no implicit cast from your enums into integer values.

score 0 · Accepted Answer · answered Apr 11 '13 at 14:20

Ok, making some proofs I have finally solved it using overload. I've removed the ObjectTypes by overloading the method and creating three different structs:

struct KeyboardTypes {
   enum types{
      DEFAULT
   };
};
struct MouseTypes {
   enum types{
      DEFAULT,
      INVERSE
   };
};
struct HapticTypes {
   enum types{
      DEFAULT
   };
};

And the overloaded member function:

void changeInputSystem(SimulatorConstants::MouseTypes::types type);
void changeInputSystem(SimulatorConstants::KeyboardTypes::types type);
void changeInputSystem(SimulatorConstants::HapticTypes::types type);

Thanks to everyone who has helped.

Enum inside enum on C++

3 Answers3