程式碼：

#include <iostream>
using namespace std;

class Animal
{
public:
    virtual void makeSound() { cout << "rawr" << endl; }
};

class Dog : public Animal
{
public:
    virtual void makeSound() {cout << "bark" << endl;}
};

int main()
{
    Animal animal;
    animal.makeSound(); // rawr (1)
 


    Dog dog;
    dog.makeSound();  // bark (2)

    Animal badDog = Dog();
    badDog.makeSound();  // (3) rawr !!!!!!!!!!!!!!!!!!!

    Animal* goodDog = new Dog();
    goodDog->makeSound();  // bark (4)
}

定義了一個Animal類，派生類Dog，如果不使用指標或引用，badDog的型別永遠是Animal型別，而不會是別的型別。Animal badDog = Dog()將一個新的Dog物件複製到badDog