60.cpp

#include <iostream>
using namespace std;
class base {
    public:
        virtual void vfunc() 
        {
            cout << "This is base's vfunc().\n";
        }
};
class derived1 : public base {
    public:
        void vfunc() 
        {
            cout << "This is derived1's vfunc().\n";
        }

};

class derived2 : public base {
    public:
        void vfunc() 
        {
            cout << "This is derived2's vfunc().\n";
        }
};

int main()
{
    base *p, b;
    derived1 d1;
    derived2 d2;

//    derived1 *p2;				
//    p2 = &b;				//error
    
    d1.vfunc();
    d2.vfunc();
    // point to base
    p = &b;
    p->vfunc(); // access base's vfunc()
    // point to derived1
    p = &d1;
    p->vfunc(); // access derived1's vfunc()
    // point to derived2
    p = &d2;
    p->vfunc(); // access derived2's vfunc()
    return 0;
}