Question

I have the code below:

class A
{
};

class B: public virtual A
{
public:
    B()
    {
        cerr << "B()";
    }
    B(const A& a)
    {
        cerr << "B(const A&)";
    }
};

class C: public B
{

};

int main(int argc, char **argv)
{
    B *b = new B(C());
}

To my surprise B(const A& a) isn’t called. Why is that?

Answer 1

B also has an implicitly declared copy constructor that is declared as

B(const B&);

This implicitly declared member function is called because it is a better match for the argument of type C than your user-declared constructor, B(const A&).