How to call copy constructor of all base classes for copying most derived class object in diamond inheritance in C++?

Question

Consider the below code:

#include
using namespace std;
class A
{
public:
     A() {cout << \"1\";}
     A(const A &obj) {cout <<          


        

Answer 1

The way you have inherited your classes, all of them use private inheritance.

By changing the inheritance of B from A and C from A to be protected or public, you can resolve the problem.

class B : protected virtual A
{
   ...
}

class C : protected virtual A
{
   ...
}

or

class B : public virtual A
{
   ...
}

class C : public virtual A
{
   ...
}

and then update D's copy constructor to:

D(const D & obj) : A(obj), B(obj), C(obj) {cout <<"8";}

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PS It's baffling to me that the default constructor works even with private inheritance.