Question

I have the following code

class nest_empty
{
   class empty{};
};

Will the size of nest_empty be 1 (on my implementation sizof an empty class is 1)? If yes why? Can nest_empty be considered as an empty class?

EDIT:

class nest_empty
{
   class empty{};
   empty d;
};

Will the size of nest_empty still be 1? If yes why?

Answer 1

Your first version of nest_empty is an empty class (no non-static data members, and no non-empty bases), so if they have size 1 in your implementation, it has size 1.

“Why” is because empty classes have size 1 on your implementation, which in turn is because they can’t have size 0 (the standard forbids it), and your implementer has chosen 1.

Your second nest_empty is not an empty class (it has a non-static data member). It could legally have size 1, since its only non-static data member, d, is of type empty, which is an empty class and hence presumably of size 1.

I can’t tell you whether it actually will have size 1 on your implementation, though. Ask your compiler.