源程序：
#include <iostream>
using namespace std;
class Base
{
public:
virtual void display() = 0;
};
class Derived1 :public Base
{
public:
void display()
{
cout << "Derived1 called" << endl;
}
};
class Derived2 :public Base
{
public:
void display()
{
cout << "Derived2 called" << endl;
}
};
void fun(Base *p)
{
p->display();
}
int main()
{
Derived1 b1;
Derived2 b2;
Base *p = &b1;
fun(p);
p = &b2;
fun(p);
system("pause");
return 1;
}
运行结果：
