OOP c++ virtual

virtual-fixed.cpp

#include <vector>
#include <iostream>

class A {
private:
	std::vector<int> data_;

public:
	A()
	{
		std::cout << "A()" << std::endl;
	}

	A(const std::vector<int>& data) :
		data_(data)
	{
		std::cout << "A(data)" << std::endl;
	}

	std::vector<int> GetData() const {
		return this->data_;
	}
};

class B : public A {
private:
	int number_1_;
	int number_2_;

public:
	B()
	{
		std::cout << "B()" << std::endl;
	}

	B(int number_1, int number_2, const std::vector<int>& data) :
		number_1_(number_1),
		number_2_(number_2),
		A(data)
	{
		std::cout << "B(number_1, number_2, data)" << std::endl;
	}

	int GetN1() const {
		return number_1_;
	}

	int GetN2() const {
		return number_2_;
	}
};

class C : virtual public B {
private:
	C(int number, const std::vector<int>& data) :
		B(number, number, data)
	{
		std::cout << "C(number, data)" << std::endl;
	}

public:
	C()
	{
		std::cout << "C()" << std::endl;
	}

	C(const std::vector<int>& data) :
		C(data.size(), data)
	{
		std::cout << "C(data)" << std::endl;
	}
};

class D : public C {
private:
	D(int number, const std::vector<int>& data) :
		B(number, number, data)
	{
		std::cout << "D(number, data)" << std::endl;
	}
public:
	D(const std::vector<int>& data) :
		D(data.size(), data)
	{
		std::cout << "D(data)" << std::endl;
	}
};

int main() {
	D d({1,2,3,4});
	std::cout << "d.GetData().size() " << d.GetData().size() << std::endl; // 4
	std::cout << "d.GetN1() " << d.GetN1() << std::endl; // 4
	std::cout << "d.GetN2() " << d.GetN2() << std::endl; // 4

	return 0;
}

virtual-fixme.cpp

#include <vector>
#include <iostream>

class A {
private:
	std::vector<int> data_;

public:
	A()
	{
		std::cout << "A()" << std::endl;
	}

	A(const std::vector<int>& data) :
		data_(data)
	{
		std::cout << "A(data)" << std::endl;
	}

	std::vector<int> GetData() const {
		return this->data_;
	}
};

class B : public A {
private:
	int number_1_;
	int number_2_;

public:
	B()
	{
		std::cout << "B()" << std::endl;
	}

	B(int number_1, int number_2, const std::vector<int>& data) :
		number_1_(number_1),
		number_2_(number_2),
		A(data)
	{
		std::cout << "B(number_1, number_2, data)" << std::endl;
	}

	int GetN1() const {
		return number_1_;
	}

	int GetN2() const {
		return number_2_;
	}
};

class C : virtual public B {
private:
	C(int number, const std::vector<int>& data) :
		B(number, number, data)
	{
		std::cout << "C(number, data)" << std::endl;
	}

public:
	C()
	{
		std::cout << "C()" << std::endl;
	}

	C(const std::vector<int>& data) :
		C(data.size(), data)
	{
		std::cout << "C(data)" << std::endl;
	}
};

class D : public C {
public:
	D(const std::vector<int>& data) :
		C(data)
	{
		std::cout << "D(data)" << std::endl;
	}
};

int main() {
	D d({1,2,3,4});
	std::cout << "d.GetData().size() " << d.GetData().size() << std::endl; // 0
	std::cout << "d.GetN1() " << d.GetN1() << std::endl; // undefined
	std::cout << "d.GetN2() " << d.GetN2() << std::endl; // undefined

	return 0;
}

virtual.cpp.diff

#include <vector>
#include <iostream>

class A {
private:
	std::vector<int> data_;

public:
	A()
	{
		std::cout << "A()" << std::endl;
	}

	A(const std::vector<int>& data) :
		data_(data)
	{
		std::cout << "A(data)" << std::endl;
	}

	std::vector<int> GetData() const {
		return this->data_;
	}
};

class B : public A {
private:
	int number_1_;
	int number_2_;
public:
	B()
	{
		std::cout << "B()" << std::endl;
	}

	B(int number_1, int number_2, const std::vector<int>& data) :
		number_1_(number_1),
		number_2_(number_2),
		A(data)
	{
		std::cout << "B(number_1, number_2, data)" << std::endl;
	}

	int GetN1() const {
		return number_1_;
	}

	int GetN2() const {
		return number_2_;
	}
};

class C : virtual public B {
private:
	C(int number, const std::vector<int>& data) :
		B(number, number, data)
	{
		std::cout << "C(number, data)" << std::endl;
	}

public:
	C()
	{
		std::cout << "C()" << std::endl;
	}

	C(const std::vector<int>& data) :
		C(data.size(), data)
	{
		std::cout << "C(data)" << std::endl;
	}
};

class D : public C {
+ private:
+	D(int number, const std::vector<int>& data) :
+		B(number, number, data)
+	{
+		std::cout << "D(number, data)" << std::endl;
+	}
public:
	D(const std::vector<int>& data) :
-               C(data)
+               D(data.size(), data)
	{
		std::cout << "D(data)" << std::endl;
	}
};

int main() {
	D d({1,2,3,4});
	std::cout << "d.GetData().size() " << d.GetData().size() << std::endl; // 4
	std::cout << "d.GetN1() " << d.GetN1() << std::endl; // 4
	std::cout << "d.GetN2() " << d.GetN2() << std::endl; // 4

	return 0;
}