Question

This code works with clang but g++ says:

error: ‘A::A()’ is protected

class A
{
protected:
    A() {}
};

class B : public A
{
    static A f() { return A(); } // GCC claims this is an error
};

Which compiler is right?

Answer 1

g++ is right.

The C++ Standard §11.5/1 says that “<…> the access must be through a pointer to, reference to, or object of the derived class itself <…>”. In case of constructors, this means that B is allowed to call the protected constructor of A only in order to construct its own base subobject.

Check this related issue in g++. It was closed as not a bug.