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Question #133 Difficulty: 2

According to the C++23 standard, what is the output of this program? 

    #include <iostream>

class A
{
public:
    A() { std::cout << "A"; }
    A(const A &) { std::cout << "a"; }
};

class B: public virtual A
{
public:
    B() { std::cout << "B"; }
    B(const B &) { std::cout << "b"; }
};

class C: public virtual A
{
public:
    C() { std::cout << "C"; }
    C(const C &) { std::cout << "c"; }
};

class D: B, C
{
public:
    D() { std::cout << "D"; }
    D(const D &) { std::cout << "d"; }
};

int main()
{
    D d1;
    D d2(d1);
}

Hint:

Virtual inheritance is a technique used to avoid multiple copies of the same indirect base class in an object.

The call order of base constructors is well-defined.

Answer:

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