MAIN.CPP

#include <iostream>
#include "Pet.h"
#include "Cat.h"
#include "Dog.h"
using namespace std;

int main() {
	setlocale(LC_ALL, "rus");
	Pet *cat, *dog, *bee;
	Cat matroskin;
	Dog sharik;
	cat = &matroskin;
	dog = &sharik;
	cat->voice();
	dog->voice();
	return 0;
}

PET.H

#pragma once
class Pet
{
public:
	Pet();
	virtual void voice() = 0;
};

CAT.H

#pragma once
#include <iostream>
#include "Pet.h"
class Cat : virtual public Pet
{
public:
	Cat();
	virtual void voice() {
		std::cout << "Мяв\n";
	}
};

DOG.H

#pragma once
#include <iostream>
#include "Pet.h"
class Dog : virtual public Pet
{
public:
	Dog();
	virtual void voice() {
		std::cout << "Гав\n";
	}
};