程序代码：

#include"iostream.h"
class base
{
public:
    virtual ~base() {}
    virtual void func()
    {
    cout<<"base output!"<<endl;
    }
};
class derived1:public base
{
public:
    void func()
    {cout<<"derived1 output!"<<endl;
    }
};
class derived2:public derived1
{
public:
    void func()
    {cout<<"derived2 output!"<<endl;
    }
};
void test ( base &rBase)
{
rBase.func();
};
void main()
{
base bObj;
derived1 d1Obj;
derived2 d2Obj;
test(bObj);
test(d1Obj);
test(d2Obj);
}