#include<iostream>
using namespace std;

class base
{
public:
virtual void f1()
{
cout<<"f1 base"<<endl;
}
virtual void f2()
{
cout<<"f2 base"<<endl;
}
void f3()
{
cout<<"f3 base"<<endl;
}
};

class derive:public base
{
private:
void f1()
{
cout<<"f1 derive"<<endl;
}
void f2(int x)
{
cout<<"f2 derive"<<endl;
}
void f3()
{
cout<<"f3 derive"<<endl;
}
};

int main()
{
base ob1,*p;
derive ob2;
p=&ob1;
p->f1();
p->f2();
p->f3();
p=&ob2;
p->f1();
p->f2();
p->f3();
return 0;
}

为什么类derive的私有成员函数，也可以直接访问啊？

可以啊，你看我主函数里写的．

int main()
{
base ob1,*p;
derive ob2;
p=&ob1;
p->f1();
p->f2();
p->f3();
p=&ob2;
p->f1();
p->f2();
p->f3();
return 0;
}