c++虚函数几种实现方法

#include <fstream>
#include <iostream>
#include <string>
#include <vector>

struct Base {
    virtual void f() { std::cout << "base" << std::endl; }
    virtual void init() {}
    Base() {
        init(); 
    }
};

struct Derived : Base { //结构体默认为public 继承, 类默认为 private
    void f() override { //加入override关键字,表示重写基类的f()虚函数
        std::cout << "derived overide" << std::endl;
    }
    void init() override { std::cout << "virtual init" << std::endl; }
} ;

struct Derived2 : Derived {
    public:
        void f() {}
        void init() {}
};

Base* factoryBase(int type) {
    Base* ret = nullptr;
    if(type == 0) {
        ret = new Base();   
    }else if(type == 1) {
        ret = new Derived();    
    }else if(type == 2) {
        ret = new Derived2();   
    }

    if(ret) ret->init();
    return ret;
}

void testVirtual() {
    //Base b;
    //Derived d;
    ////虚函数调用通过引用
    ////virtual funciton call through reference
    //Base& br = b;  //the type of br is Base&
    //Base& dr = d;  //the type of dr is Base& as well
    //br.f();
    //dr.f(); //在Derived类中已经对fun() 重写.
    //
    ////虚函数调用通过指针
    ////virtual function call through pointer
    //Base* bp = &b;
    //Base* dp = &d;
    //bp->f();
    //dp->f();

    ////直接调用.
    ////non-virtual function call
    //b.Base::f();
    //d.Derived::f(); //派生类
    //d.Base::f(); //基类
    ////若在构造函数中或者析构函数中调用虚函数, 则会调用自身类中的虚函数,而不是派生类的重写的虚函数
    ////虚函数特性还没体现
    Derived d;
}
int main(void) {
    testVirtual();
    return 0;
}