How to avoid name conflicts for two enum values with the same name in C++?

Question

Enums in C++ have one major problem: You can't have one name in two different enums like this:

enum Browser
{
    None = 0,
    Chrome = 1,
    Firefox = 2
}

enum OS
{
    None = 0,
    XP = 1,
    Windows7 = 2
}

So what is the best way to handle this issue in this example?

If the enum is specific to a class, place it inside a (public section of) the class, then refer to the elements by e.g. ClassName::None and OtherClassName::None. You can also put the enums in namespaces instead. The typical way to namespace them in pure C is via prefixes to each enumerated identifier. — pmdj, Jun 03 '12 at 11:12
My question http://stackoverflow.com/questions/12972317/count-on-enum-c-automatic answers your question. — sergiol, Oct 20 '12 at 15:58
enum classes in C++ 11 seem to be a good attempt. But you have to cast it after applying `|`. — bytecode77, Oct 20 '12 at 16:02

score 32 · Accepted Answer · answered Jun 03 '12 at 11:11

32

In C++03 you can enclose enum inside a struct:

struct Browser
{
  enum eBrowser
  {
    None = 0,
    Chrome = 1,
    Firefox = 2
  };
};

In C++11 make it an enum class:

enum class Browser
{
    None = 0,
    Chrome = 1,
    Firefox = 2
};

In C++03 namespace also can be wrapped, but personally I find wrapping struct/class better because namespace is more broader. e.g.

// file1.h
namespace X
{
  enum E { OK };
}

// file2.h
namespace X
{
  enum D { OK };
}

answered Jun 03 '12 at 11:11

iammilind

68,093
33
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Why `struct` and not `namespace`? – Pubby Jun 03 '12 at 11:11
1

@Pubby, `namespace` is also ok, but I find `struct`/`class` "philosophically" more compatible with `enum class`. – iammilind Jun 03 '12 at 11:12
4

@Pubby: You can specialize templates on `struct`. – Matthieu M. Jun 03 '12 at 11:46

score 13 · Answer 2 · answered Jun 03 '12 at 11:12

One option is to put each enum in a different namespace:

namespace Foo {
  enum Browser {
      None = 0,
      Chrome = 1,
      Firefox = 2
  }
}

namespace Bar {
  enum OS {
      None = 0,
      XP = 1,
      Windows7 = 2
  }
}

A better option, if available with your compiler, is to use C++11 enum classes:

enum class Browser { ... }
enum class OS { ... }

See here for a discussion on enum classes.

score 3 · Answer 3 · answered Jun 03 '12 at 11:10

3

Either wrap them in namespaces or in classes:

namespace Browser {
  enum BrowserType
  {
    None = 0,
    Chrome = 1,
    Firefox = 2
  }
}

namespace OS {
   enum OSType  {
      None = 0,
      XP = 1,
      Windows7 = 2
  }
}

answered Jun 03 '12 at 11:10

Not_a_Golfer

47,012
14
126
92

score 2 · Answer 4 · edited Jul 30 '16 at 13:05

2

You can use enum class (scoped enums) which is supported in C++11 on up. It is strongly typed and indicates that each enum type is different.

Browser::None != OS::None   

enum class Browser
{
    None = 0,
    Chrome = 1,
    Firefox = 2
}

enum class OS
{
    None = 0,
    XP = 1,
    Windows7 = 2
}

edited Jul 30 '16 at 13:05

Patryk

22,602
44
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244

answered Nov 07 '14 at 15:12

DML

494
5
4

score 1 · Answer 5 · answered Jan 28 '13 at 01:15

1

How about using scoped vs. unscoped enumeration? c++11 now offers scoped enumeration. An example would be:

enum class Browser : <type> {

};

enum class OS : <type> {

};

Access the enumerated types via an object of the Browser or an object of OS.

answered Jan 28 '13 at 01:15

user633658

2,463
2
18
16

How to avoid name conflicts for two enum values with the same name in C++?

5 Answers5

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