面向对象程序设计-C++ Class & Object & Friend Function & Constructor & Destructor【第五次上课笔记】

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以下代码均已折叠，点击“+“即可打开

一开始老师用C语言大作业的例子，写了个 Student 的结构以及相关操作

 #include <iostream>
 #include "Student.h"

 using namespace std;

 void display (Student* s) {
     cout << "The current information of student:" << endl
         << "\tBirthday is " << s->birth.year << "-" << s->birth.month << "-" << s->birth.day << endl
         << "\tName is " << s->name << endl;
 }

 void edit (Student* s, char* n){
     /*
     int i;
     for (i = 0; n[i] != 0; ++i) {
         s->name[i] = n[i];
     }
     s->name[i] = 0;
     */
     s->name = n;
 }

 int main(){

     Date date;
     date.year = ;
     date.month = ;
     date.day = ;
     Student stu;
     stu.birth = date;
     stu.name = "Zhang San";    //Exist problems

     display (&stu);

     edit (&stu, "Li Si");

     display (&stu);

     return ;
 }

SourceCode.cpp

 struct Date {
     int year, month, day;
 };

 struct Student {
     Date birth;
     char* name;
 };

Student.h

不难发现，这份代码在

	stu.name = "Zhang San";	//Exist problems

　存在空间未分配的问题，还去赋值，暂时不管它

接着老师讲了正确姿势的写法，就是“初始化分配空间、结束的时候清空”的写法

 #include <iostream>
 #include <cstring>
 #include "Student.h"

 using namespace std;

 void display (Student* s) {
     cout << "The current information of student:" << endl
         << "\tBirthday is " << s->birth.year << "-" << s->birth.month << "-" << s->birth.day << endl
         << "\tName is " << s->name << endl;
 }

 void edit (Student* s, char* n){
     /*
     int i;
     for (i = 0; n[i] != 0; ++i) {
         s->name[i] = n[i];
     }
     s->name[i] = 0;
     */
     //s->name = n;

     if (NULL != s->name)    //if s->name is not NULL
         delete[] s->name;

     int len = strlen (n);
     s->name = new char[len + ];
     strcpy (s->name, n);    

 }

 void initialize (Student* s, Date* d, char* n) {
     s->birth.year = d->year;
     s->birth.month = d->month;
     s->birth.day = d->day;

     int len = strlen (n);
     s->name = new char[len + ];
     strcpy (s->name, n);
     //s->name = n;
 }

 void clean (Student* s) {
     delete[] s->name;
 }

 int main(){

     Date date;
     date.day = ;
     date.month = ;
     date.year = ;
     Student stu;
     initialize (&stu, &date, "Zhang San");

     display (&stu);
     edit (&stu, "Li Si");
     display (&stu);

     clean (&stu);

     return ;
 }

SourceCode.cpp

 struct Date {
     int year, month, day;
 };

 struct Student {
     Date birth;
     char* name;

     //void edit ();
     //void display ();
 };

Student.h

接下来，开始介绍了C++中面向对象的方法，使用 类来操作，同时把原来的函数都写进类使其成为成员函数

C++单文件版本：

 #include <iostream>
 #include <cstring>

 using std::cout;    //也可以这么写
 using std::endl;    //ADD

 struct Date {
     int year, month, day;
 };

 class Student {
 private:    //成员的访问控制
     Date birth;
     char* name;

 public:
     void edit (char* n);    //成员函数
     void display ();
     void initialize (Date* d, char* n);
     void clean ();
 };

 void Student::edit (char* n) { // :: means Scope operation
     if (NULL != name)    //if s->name is not NULL
         delete[] name;

     int len = strlen (n);
     name = new char[len + ];
     strcpy (name, n);
 }

 void Student::display () {
     cout << "The current information of student:" << endl
         << "\tBirthday is " << birth.year << "-" << birth.month << "-" << birth.day << endl
         << "\tName is " << name << endl;
 }

 void Student::initialize (Date* d, char* n) {
     birth.year = d->year;
     birth.month = d->month;
     birth.day = d->day;

     int len = strlen (n);
     name = new char[len + ];
     strcpy (name, n);
 }

 void Student::clean () {
     if (NULL != name)
         delete[] name;
 }

 int main(){

     Date date;
     date.day = ;
     date.month = ;
     date.year = ;
     Student stu;

     stu.initialize (&date, "Zhang San");

     stu.display ();
     stu.edit ("Li Si");
     stu.display ();

     stu.clean ();

     return ;
 }

SourceCode.cpp

老师也提到，在我们实际开发过程中是不会这么只一个cpp文件的，肯定是多文件

因为我注释写的比较详细，具体可以看以下代码：

Student.h

　　

 #ifndef STUDENT_H    //编译预处理
 #define STUDENT_H    //防止多次包含头文件

 struct Date {
     int year, month, day;
 };

 class Student {

 private:    //成员的访问控制
     Date birth;
     char* name;

 public:
     void edit (char* n);    //成员函数
     void display ();
     //void initialize (Date* d, char* n);
     void clean ();

     //friend void frimen ();    //友元函数

     Student (Date* d, char* n);
     Student ();
 };

 //void frimen () {
 //    Student stu;
 //    stu.birth.day = 16;
 //}

 #endif

student.cpp

　　

 #include <iostream>
 #include <cstring>
 #include "student.h"

 using std::cout;    //也可以这么写
 using std::endl;    //ADD

 void Student::edit (char* n) { // :: means Scope operation
     if (NULL != name)    //if s->name is not NULL
         delete[] name;

     int len = strlen (n);
     name = new char[len + ];
     strcpy (name, n);
 }

 void Student::display () {
     cout << "The current information of student:" << endl
         << "\tBirthday is " << birth.year << "-" << birth.month << "-" << birth.day << endl
         << "\tName is " << name << endl;
 }

 Student::Student (Date* d, char* n) { //后面的Student表示，这个函数是构造函数
     birth.year = d->year;
     birth.month = d->month;
     birth.day = d->day;

     int len = strlen (n);
     name = new char[len + ];
     strcpy (name, n);
 }

 Student::Student () {
     cout << "Student::Student () is Called" << endl;
 }

 void Student::clean () {
     if (NULL != name)
         delete[] name;
 }

SourceCode.cpp

　　

 #include <iostream>
 #include <cstring>
 #include "student.h"

 int main(){

     Date date;
     date.day = ;
     date.month = ;
     date.year = ;
     Student stu (&date, "Zhnag San");    //init

     Student stu2;

     //stu.initialize (&date, "Zhang San");

     stu.display ();
     stu.edit ("Li Si");
     //stu.birth.year = 1989;    //Cannot access private member declared in class 'Student'
     stu.display ();

     stu.clean ();

     return ;
 }