CODEWITHSUNDEEP
c++enumsnamespacesc++11
Stals
Stals

Reputation: 1603

enum in a namespace

Is there a point of doing somthing like this:

namespace status{
  enum status{
    ok,
    error
  };
}

and use it like that status::ok

Or should i do this:

enum status{
  status_ok,
  status_error
};

and use it like this status_ok?

Update: With C++11 you now should do this:

enum class status {
    ok,
    error
};

and use like this: status::ok

Upvotes: 23

Views: 20565

Answers (5)

Frerich Raabe
Frerich Raabe

Reputation: 94299

I personally don't like the second variation because the status_ part seems redundant to me. The former version avoids that problem, but having a type status::status looks strange too. Furthermore, a namespace is open to modification, so in case somebody did something like

namespace status {
  void error( const char *msg );
}

You would get a compiler error since the function error clashes with your enum value.

I prefer to use a third variation:

struct MouseButton {
  enum Value {
    Left, Middle, Right
  };
};

This lets me write functions like

void handleMouseButton( MouseButton::Value b ) {
  switch ( b ) {
    case MouseButton::Left:   // ...
    case MouseButton::Middle: // ...
    case MouseButton::Right:  // ...
  }
}

Upvotes: 22

neodelphi
neodelphi

Reputation: 2786

What you want has just been added to C++ when enabling C++0x extensions. However, if you cannot use C++0x features, I suggest to do this:

struct status
{
    enum value
    {
        ok,
        error
    };
};

With a such declaration you can write:

status::value var = status::ok;

Such a structure will also allow you to declare functions related to the status type inside the struct scope. For example, the status struct could contain methods to convert to/from a string.

Upvotes: 7

iammilind
iammilind

Reputation: 69988

If you are not worried about using enum status type as such, then you can keep it anonymous.

namespace status{
  enum {  // <--- no name
    ok,
    error
  };
}

Upvotes: 4

Dan
Dan

Reputation: 13382

Firstly you should access enums using the scope operator, :: not the dot . operator; i.e. status::ok

Both are fine it's what you feel would be more readable. Note you can also use (without the namespace)

enum status{
   ok,
   error
}

and still use status::ok but some compilers will warn you that the extra status:: is unnecessary.

EDIT: Accessing an enum using :: seems to work only with MS visual-c++

Upvotes: 1

Pieter
Pieter

Reputation: 17705

I prefer the namespace approach, as it allows using namespace and using the shorter enum values if only one enum is used in a piece of code.

It's mostly a matter of personal preference, however, I feel that solving (potential) name clashes in C++ is best done using namespaces, as that's the point of having namespaces in the first place.

Upvotes: 1

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