例11.10 定義一個(gè)基類Student(學(xué)生)，再定義Student類的公用派生類Graduate(研究生)，用指向基類對(duì)象的指針輸出數(shù)據(jù)。
本例主要是說(shuō)明用指向基類對(duì)象的指針指向派生類對(duì)象，為了減少程序長(zhǎng)度，在每個(gè)類中只設(shè)很少成員。學(xué)生類只設(shè)num(學(xué)號(hào)),name(名字)和score(成績(jī))3個(gè)數(shù)據(jù)成員，Graduate類只增加一個(gè)數(shù)據(jù)成員pay(工資)。程序如下:
#include <iostream>
#include <string>
using namespace std;
class Student//聲明Student類
{public:
   Student(int, string,float);                       //聲明構(gòu)造函數(shù)
   void display( );                                   //聲明輸出函數(shù)
private:
   int num;
   string name;
   float score;
};

Student::Student(int n, string nam,float s)          //定義構(gòu)造函數(shù)
{num=n;
  name=nam;
  score=s;
}

void Student::display( )                             //定義輸出函數(shù)
{cout<<endl<<″num:″<<num<<endl;
  cout<<″name:″<<name<<endl;
  cout<<″score:″<<score<<endl;
}

class Graduate:public Student                    //聲明公用派生類Graduate
{public:
  Graduate(int, string ,float,float);             //聲明構(gòu)造函數(shù)
  void display( );                                 //聲明輸出函數(shù)
private:
  float pay;                                      //工資
};

Graduate::Graduate(int n, string nam,float s,float p):Student(n,nam,s),pay(p){ }
                                         //定義構(gòu)造函數(shù)
void Graduate::display()                             //定義輸出函數(shù)
{Student::display();                          //調(diào)用Student類的display函數(shù)
  cout<<″pay=″<<pay<<endl;
}

int main()
 {Student stud1(1001,″Li″,87.5);                 //定義Student類對(duì)象stud1
  Graduate grad1(2001,″Wang″,98.5,563.5);        //定義Graduate類對(duì)象grad1
  Student *pt=&stud1;//定義指向Student類對(duì)象的指針并指向stud1
  pt->display( );                 //調(diào)用stud1.display函數(shù)
  pt=&grad1;                     //指針指向grad1
  pt->display( );                 //調(diào)用grad1.display函數(shù)
 }