C++多态性需要帮助

Question

我不得不在类(class)人员和类(class)学生之间进行继承，然后使用多态指针 pIndividual 编写测试程序。该程序可以编译，但不会为我列出 student1 的统计信息。

这是我的代码:

    #include <iostream>
    #include <string>

    using namespace std;

    class Person
    {
    public:
         string m_Name, m_Address, m_City, m_State;
         int m_Zip, m_Phone_Number;

         void virtual list_stats();
    };

     void Person::list_stats()
     {
           cout << "This is the function show_stats() that is in class Person to show   person1's " << endl;
          cout << "information:" << endl << endl;
          cout << "Name: " << m_Name << endl << "Address: " << m_Address << endl << "City: " << m_City << endl; 
          cout << "State: " << m_State << endl << "Zip: " << m_Zip << endl << "Phone Number: " << m_Phone_Number << endl << endl;
      }

      class Student : public Person
      {
      public:
            char m_Grade;
            string m_Course;
            float m_GPA;
            void virtual list_stats();

           Student(float GPA = 4.0);
      };

      Student::Student(float GPA)
      {
           m_GPA = GPA;
      }

      void Student::list_stats()
       {
          cout << "This is the function show_stats() that is in class Student to show student1's " << endl;
          cout << "information by using pointer pIndividual:" << endl << endl;
          cout << "Name: " << m_Name << endl << "Address: " << m_Address << endl << "City: " << m_City << endl; 
         cout << "State: " << m_State << endl << "Zip: " << m_Zip << endl << "Phone Number: " << m_Phone_Number << endl << endl;
   }

    int main()
      {
          Person person1;
          person1.m_Name = "Sarah";
          person1.m_Address = "ABC Blvd.";
          person1.m_City = "Sunnytown";
          person1.m_State = "FL";
          person1.m_Zip = 34555;
          person1.m_Phone_Number = 1234567;

          person1.list_stats();

          Student student1(4.0);
          student1.m_Name = "Todd";
          student1.m_Address = "123 Four Dr.";
          student1.m_City = "Anytown";
          student1.m_State = "TX";
          student1.m_Zip = 12345;
          student1.m_Phone_Number = 7654321;
          student1.m_Grade = 'A';
          student1.m_Course = "Programming";


          Person* pIndividual = new Student;
          pIndividual->list_stats();

          system("PAUSE");
          return EXIT_SUCCESS;
     }

Answer 1

因为您正在使用new 创建另一个 Student 实例。这个默认构造的实例没有任何数据集。你需要:

Person* pIndividual = &student1;

获取指向您创建的 student1 的指针，并在调用 list_stats() 时查看其数据。