如何在所有派生类中调用overriden方法

class Animal {
public:
    virtual void speak() {
        std::cout << "I'm an animal." << std::endl;
    }
};

class Dog : public Animal {
public:
    void speak() override {
        std::cout << "I'm a dog." << std::endl;
    }
};

class Cat : public Animal {
public:
    void speak() override {
        std::cout << "I'm a cat." << std::endl;
    }
};

int main() {
    Animal myAnimal;
    Dog myDog;
    Cat myCat;

    myAnimal.speak(); // 输出 "I'm an animal."
    myDog.speak();    // 输出 "I'm a dog."
    myCat.speak();    // 输出 "I'm a cat."
}