CODEWITHSUNDEEP
classc++11enums
ge45mue
ge45mue

Reputation: 707

Split declaration and defintion of c++ enum class

I'd like to use a enum class in the following way

// Foo.h
enum class Foo : uint8_t;

with

// Foo.cpp
enum class Foo : uint8_t {
  FOO = 0,
};

// Bar.cpp
enum class Foo : uint8_t {
  FOO = 1,
};

and

// MainLinkedWithFoo.cpp
#include "Foo.h"
int main () {
  (void)Foo::FOO;
  return 0;
}

// MainLinkedWithBar.cpp
#include "Foo.h"
int main () {
  (void)Foo::FOO;
  return 0;
}

But I get following error

incomplete type 'Foo' named in nested name specifier

Does somebody know how to solve this "problem"?

Thanks

Upvotes: 0

Views: 1461

Answers (1)

lubgr
lubgr

Reputation: 38277

You can forward-declare scoped enums, but at the time you refer to the actual enumeration identifiers (e.g. Foo::FOO), the complete enum definition must be available to the compiler.

Most often, scoped enums are neither an implementation details passed through interfaces nor a bottleneck for your compile times. Hence, the straightforward fix is to put the definition into the header file.

// Foo.h
enum class Foo : uint8_t {
  FOO = 0,
  BAR = 1
};

But as you explicitly asked for separate declaration and definition, you might want this:

// FooFwd.h
enum class Foo : uint8_t;

and the definition in Foo.h as above. Then, whenever you want to use an enumeration instance without referring its actual enumerators, you can just #include "FooFwd.h", and if you need access to e.g. Foo::FOO, go with #include "Foo.h".

Upvotes: 1

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