先是自己凭借自己在课堂上的记忆打了一遍。自然出了错误。

//编译错误#include 
    
     #include 
     
      using namespace std;class people{    private:        int age;        int sex; // 1 -girl 2 -boy    public:        people(int a = 0, int b = 0): age(a), sex(b){};};class student : public people{    private:        int num;        int score;        string name;    public:        student(int bnum = 0, int bscore = 0, int bage = 0, int bsex = 0, string bname):people(bage, bsex) //错误        {            num = bnum;            score = bscore;            name = bname;        };                void display();};void student::display(){    if(sex == 1) //错误    cout << name << " girl " << num << " " << age << " " << score << endl;    else     cout << name << " boy " << num << " " << age << " " << score << endl;}int main(){    student Liming(10001, 100, 20, 2, "李鸣");    Liming.display() ;        return 0;}
     
    

错误小结：    1.类student是public继承于类people，那么在student的成员函数中，无法访问父类的private和protected属性的成员，只能通过继承过来的父类的成员函数访问它们。    2.初始化列表写错了。函数的默认参数最后一句 string bname; 应该是 string bname = "";

改了之后，可以运行了。

#include 
    
     #include 
     
      using namespace std;class people{    private:        int age;        int sex; // 1 -girl 2 -boy    public:        people(int a = 0, int b = 0): age(a), sex(b){};        int getage();        int getsex();};int people::getage(){    return age;}int people::getsex(){    return sex;}class student : public people{    private:        int num;        int score;        string name;    public:        student(string bname,int bnum = 0, int bscore = 0, int bage = 0, int bsex = 0)        :people(bage, bsex),num(bnum),score(bscore){name = bname;};                void display();};void student::display(){    if(getsex() == 1)    cout << name << " girl " << num << " " << getage() << " " << score << endl;    else     cout << name << " boy " << num << " " << getage() << " " << score << endl;}int main(){    student Liming("李鸣", 10001, 100, 20, 2);    Liming.display() ;        return 0;}
     
    

学习到的知识点：

1.对于父类的派生类来说，其对象的初始化需要利用初始化列表进行操作。比如：student(string bname, int bnum = 0, int bscore = 0, int bage = 0, int bsex = 0):people(bage, bsex),num(bnum),score(bscore){name = bname;};上面的语句调用了父类的初始化构造函数，所以父类的构造函数应具有含参构造函数，可以利用重载来实现。个人的习惯是：写一个含有默认参数的初始化列表。2.如果是public继承，那么在派生类的成员函数中无法访问其从父类继承过来的具有private和protected属性的成员。这个时候，可以通过调用从父类继承过来的成员函数获取其值。例如：int people::getage(){    return age;}int people::getsex(){    return sex;}···void student::display(){    if(getsex() == 1) //调用父类的成员函数    cout << name << " girl " << num << " " << getage() << " " << score << endl;    else     cout << name << " boy " << num << " " << getage() << " " << score << endl;}3.复习了一下含有默认参数的构造函数，设置默认参数时应从右向左。例如：student(int bnum = 0, int bscore = 0, int bage = 0, int bsex = 0, string bname):people(bage, bsex) //错误应为：student(int bnum = 0, int bscore = 0, int bage = 0, int bsex = 0, string bname = ""):people(bage, bsex)