C++ abuse: simple example

cpp_abuse_1.cc

// C++ abuse

#include <iostream>

using namespace std;

class Animal {
public:
  virtual void food() = 0;
  virtual void sound() = 0;
};

class Dog : public Animal {
public:
  void food() { cout << "Alpo" << endl; }
  void sound() { cout << "Woof!" << endl; }
};

class Cat : public Animal {
public:
  void food() { cout << "Purina" << endl; }
  void sound() { cout << "Meow!" << endl; }
};

void transmigrate(void *dest, void *src) {
  *(void **)dest = *(void **)src;
}

void brain_damage(void *obj) {
  void *t = **((void ***)obj);
  **((void ***)obj) = *(*((void ***)obj)+1);
  *(*((void ***) obj)+1) = t;
}

// What does this program output and why?
int main() {
  Dog *dog = new Dog();
  Cat *cat = new Cat();

  dog->food();

  transmigrate(dog, cat);
  dog->food();

  brain_damage(dog);
  dog->food();
}

Something I wrote up back in the 1990s when I was first learning C++ and trying to understand it.