文章标题

子类和基类对象函数调用过程中vitual关键字的作用
感觉有些文档写得很不明确，简要总结一下
基类对象调用函数
1、如果没有virtual函数修饰
直接调用基类的函数
2、如果有virtual函数修饰
1>、如果是是通过将子类的指针或者引用传给基类的指针或者引用，例如pBase = pDerive 或者 Base &base = derive，
根据实际情况调用
I、如果子类重写了这个函数，那么执行子类的函数
II、如果子类没有重写这个函数，那么执行基类的函数
2>、如果不是第一种情况，那么执行基类的对应的函数
子类对象调用函数
1、如果子类重写了某个基类的函数
直接调用子类的这个成员函数
2、如果子类没有重写这个基类的函数
调用基类对应的函数

对应函数代码

Base.h

#pragma once#include <iostream>using namespace std;class Base{public:    Base(void);    ~Base(void);    /*    基类对象调用函数    1、如果没有virtual函数修饰        直接调用基类的函数    2、如果有virtual函数修饰        1>、如果是是通过将子类的指针或者引用传给基类的指针或者引用，例如pBase = pDerive 或者 Base &base = derive，        根据实际情况调用            I、如果子类重写了这个函数，那么执行子类的函数            II、如果子类没有重写这个函数，那么执行基类的函数        2>、如果不是第一种情况，那么执行基类的对应的函数    子类对象调用函数    1、如果子类重写了某个基类的函数        直接调用子类的这个成员函数    2、如果子类没有重写这个基类的函数        调用基类对应的函数    */    void printMsg()                 // 子类重写了    {        cout<<"Base Class"<<endl;    }    void display()                  // 子类么有重写    {        cout<<"Base display"<<endl;    }    virtual void showMsg()    {        cout<<"Base showMsg"<<endl; // 子类有重写    }    virtual void childNotHaveVir()  // 子类无重写    {        cout<<"Base childNotHaveVir"<<endl;    }};

Base.cpp

#include "Base.h"Base::Base(void){}Base::~Base(void){}

Derive.h

#pragma once#include <iostream>#include "Base.h"using namespace std;class Derive : public Base{public:    Derive(void);    ~Derive(void);    virtual void printMsg()    {        cout<<"Derive Class"<<endl;    }    //void printMsg()    //{    //  //cout<<"not virtual derived Class"<<endl;    //}    void showMsg()    {        cout<<"Derive showMsg"<<endl;    }};

Derive.cpp

#include "Derive.h"Derive::Derive(void){}Derive::~Derive(void){}

主函数

#include <iostream>#include <stdlib.h>#include <string>#include "Base.h"#include "Derive.h"using namespace std;void printMenu();void main(){    while(1)    {        printMenu();        int choice = 0;        cout<<"请选择";        cin >> choice;        cin.clear();        switch(choice)        {        case 0:            {                exit(0);            }            break;        case 1:            {                cout<<"函数名称\t子类有无\t是否为virtual"<<endl;                cout<<"printMsg\t有\t不是 "<<endl;                cout<<"display\t无\t不是 "<<endl;                cout<<"showMsg\t有\t是 "<<endl;                cout<<"childNotHaveVir\t无\t是 "<<endl;                Base base, *pBase;                Derive derive, *pDerive;                pBase = new Base;                pDerive = new Derive;                cout<<"base.printMsg()\t";                base.printMsg();                cout<<"base.display()\t";                base.printMsg();                cout<<"base.showMsg()\t";                base.showMsg();                cout<<"base.childNotHaveVir()\t";                base.childNotHaveVir();                cout<<"pBase->printMsg()\t";                pBase->printMsg();                cout<<"pBase->display()\t";                pBase->display();                cout<<"pBase->showMsg()\t";                pBase->showMsg();                cout<<"pBase->childNotHaveVir()\t";                pBase->childNotHaveVir();                cout<<"derive.printMsg()\t";                derive.printMsg();                cout<<"derive.display()\t";                derive.display();                cout<<"derive.showMsg()\t";                derive.showMsg();                cout<<"derive.childNotHaveVir()\t";                derive.childNotHaveVir();                cout<<"pDerive->printMsg()\t";                pDerive->printMsg();                cout<<"pDerive->display()\t";                pDerive->display();                cout<<"pDerive->showMsg()\t";                pDerive->showMsg();                cout<<"pDerive->childNotHaveVir()\t";                pDerive->childNotHaveVir();                Base notRefBase = derive;                cout<<"notRefBase.printMsg()\t";                notRefBase.printMsg();                cout<<"notRefBase.display()\t";                notRefBase.display();                cout<<"notRefBase.showMsg()\t";                notRefBase.showMsg();                cout<<"notRefBase.childNotHaveVir()\t";                notRefBase.childNotHaveVir();                Base &refBase = derive;                cout<<"refBase.printMsg()\t";                refBase.printMsg();                cout<<"refBase.display()\t";                refBase.display();                cout<<"refBase.showMsg()\t";                refBase.showMsg();                cout<<"refBase.childNotHaveVir()\t";                refBase.childNotHaveVir();                pBase = &derive;                cout<<"pBase->printMsg()\t";                pBase->printMsg();                cout<<"pBase->display()\t";                pBase->display();                cout<<"pBase->showMsg()\t";                pBase->showMsg();                cout<<"pBase->childNotHaveVir()\t";                pBase->childNotHaveVir();            }            break;        default:            {                cout<<"输入有误，请重新输入"<<endl;            }            break;        }    }    system("pause");}void printMenu(){    cout<<"[0] 退出"<<endl;    cout<<"[1] 继承virtual用法"<<endl;}

大家可以用上面的代码验证一下