C++11 Base constructor delegating/forwarding to derived class with "using" keyword

Question

struct B {
  B () {}
  B(int i) {}
};

struct D : B {
  using B::B;  // <--- new C++11 feature
};

D d1; // ok
D d2(3); // ok

Now, if I add a new constructor inside the body of struct D, such as:

struct D : B {
  using B::B;
  D(const char* pc) {}  // <--- added
};

then D d1; starts giving compiler error(ideone is not upgraded yet, I am using g++ 4.8.0)? However D d2(3); still works.

Why the default constructor is discounted when adding a new constructor inside struct D?

Answer 1

There is a subtle difference between

struct D : B {
 using B::B;
 D(const char* pc) {}  // <--- added
};

versus

struct D : B {
 using B::B;
};

In the second case, compiler auto-generate the default "D(){}" constructor for you. But if you create your own constructor for D, then the default "D(){}" is not available anymore. Sure you have inherited B's default constructor, but that doesn't tell the compiler how to construct D by default.