C++的虚基类与虚函数

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虚函数加vritual关键字，目的是为了实现多态性，可以通过基类的指针和引用调用派生类的对象，从而产生不同的效果。

#include<iostream>using namespace std;class Base1{    public:        virtual void display() const=0;//虚函数};class Base2:public Base1{    public:        void display() const;//覆盖基类的虚函数};void Base2::display() const{    cout<<"Base2::display()"<<endl;}class Derived:public Base2{    public:        void display() const;//覆盖基类的虚函数};void Derived::display()const{    cout<<"Dervied::display()"<<endl;};void fun(const Base1 *p){    p->display();}int main(){    Base2 base2;    Derived derived;    fun(&base2);    fun(&derived);    return 0;}

纯虚函数不能在定义类中实现，但应该在能够实例化的派生类中实现。定义了纯虚函数的类为抽象类。

#include<iostream>using namespace std;class Base1{    public:        virtual void display() const=0;//纯虚函数};class Base2:public Base1{    public:        void display() const;//覆盖基类的虚函数};void Base2::display()const{    cout<<"Base2"<<endl;}class Derived:public Base2{    public:        void display()const;//覆盖基类的虚函数};void Derived::display()const{    cout<<"Derived"<<endl;}void fun(const Base1 *p){//参数为指向基类对象的指针    p->display();}int main(){    Base2 b;    Derived d;    fun(&b);    fun(&d);    return 0;}

虚基类：虚基类是指虚继承中的基类，

#include<iostream>using namespace std;class Base0{//定义基类    public:        Base0(int v):var0(v){}        int var0;        void show() const{            cout<<var0<<endl;        }};class Base1:virtual public Base0{//Base0为虚基类    public:        Base1(int v):Base0(v){}        ~Base1(){}};class Base2:virtual public Base0{//Base0为虚基类    public:        Base2(int v):Base0(v){}};class Derived:public Base1,public Base2{    public:        Derived(int v):Base1(v),Base2(v),Base0(v){}//构造函数要从最远派生类赋值        ~Derived(){}//析构函数和普通类的构造函数没区别};int main(){    Derived d(2);    d.var0;    d.show();//直接调用虚基类的函数    return 0;}

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