#include <iostream>

 #include <cstring>

 using namespace std;

 class Base{

     public:

         virtual void func1();

         virtual void func2();

         void func3();

         void func4();

 };

 void Base::func1(){

     cout<<"Base func1"<<endl;

 }

 void Base::func2(){

     cout<<"Base func2"<<endl;

 }

 void Base::func3(){

     cout<<"Base func3"<<endl;

 }

 void Base::func4(){

     cout<<"Base func4"<<endl;

 }

 class Derived1:public Base{

     public:

         void func1();//virtual可以省略

         //char func2(){};错误，虚函数返回类型需要一致

         void func3();

         char func4();

 };

 void Derived1::func1(){

     cout<<"Derived1 func1"<<endl;

 }

 void Derived1::func3(){

     cout<<"Derived1 func3"<<endl;

 }

 char Derived1::func4(){

     cout<<"Derived1 func4 can change the return type"<<endl;

 }

 class Derived2:public Base{

     public:

         void func1();

 };

 void Derived2::func1(){

     cout<<"Derived2 func1"<<endl;

 }

 int main(){

     Base *B;

     Derived1 De1;

     B = &De1;

     B->func1();

     B->func3();

     B->func4();

     De1.func4();

     Derived2 *pDe2;

     pDe2 = (Derived2*)&De1;

     pDe2->func1();

     return ;

 }

Derived1 func1

Base func3

Base func4

Derived1 func4 can change the return type

Derived1 func1