功能呼叫在多态性调用中。虚拟功能调用

Question

以下是调用derived :: fn2（）来自derived :: fn1（），其中AS fn2（）不是虚拟的调用基类功能。谁能解释为什么？

#include <iostream>
using namespace std;

class Base{
    public:
    virtual void fn1()
    {
        cout<<"Base function 1"<<endl;
        this->fn2();
    }
    void fn2()
    {
        cout<<"Base function 2"<<endl;
    }
};


class Derived : public Base{
    public:
    
    void fn1()
    {
        cout<<"Derived function 1 "<<endl;
        this->fn2();
    }
    void fn2()
    {
        cout<<"Derived function 2"<<endl;
    }
};

int main()
{
    Base *b = new Derived();
    b->fn1();
}

Answer 1

fn2（）不是虚拟的，因此应该调用Base类的功能。

不，不应该。这就是为什么：

Derived d;

static_cast<Base&>(d).fn1();
// Calls Derived::fn1 through dynamic dispatching. In Derived::fn1, `this` is
// of type Derived*, so it will call Derived::fn2

// Output:
// Derived function 1
// Derived function 2

static_cast<Base&>(d).fn2();
// fn2() is not virtual, so you overloaded it. You're calling Base::fn2().

// Output:
// Base function 2