多态

// 父类
class ParentClass {
public:
    ParentClass() {
        doSomething();
    }
    virtual void func() {
        std::cout << "ParentClass::func() called" << std::endl;
        doSomething();
        takeSomething();
    }

protected:
    virtual void doSomething() {
        std::cout << "ParentClass::doSomething() called" << std::endl;
    }

    void takeSomething() {
        std::cout << "ParentClass::takeSomething() called" << std::endl;
    }
};

// 子类
class ChildClass : public ParentClass {
protected:
    void doSomething() override {
        std::cout << "ChildClass::doSomething() called" << std::endl;
    }
    void takeSomething() {
        std::cout << "ChildClass::takeSomething() called" << std::endl;
    }
};

int main() {
    ParentClass* parent = new ParentClass();
    parent->func();
    std::cout << std::endl;

    ChildClass* child = new ChildClass();
    child->func();

    delete parent;
    delete child;
    return 0;
}

输出

ParentClass::doSomething() called
ParentClass::func() called
ParentClass::doSomething() called
ParentClass::takeSomething() called

ParentClass::doSomething() called
ParentClass::func() called
ChildClass::doSomething() called
ParentClass::takeSomething() called

子类实例化的时候，调用父类的构造方法，在父类的构造函数中调用的方法是父类本身的。如果子类已经构造完成，调用继承的方法，这个方法中使用的函数，（要求是虚函数）如果子类有那么就是子类自身的方法。 如果不是虚函数，那么还是父类自身的方法。