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 = 1992;
    date.month = 10;
    date.day = 23;
    Student stu;
    stu.birth = date;
    stu.name = "Zhang San";    //Exist problems

    display (&stu);

    edit (&stu, "Li Si");

    display (&stu);

    return 0;
}

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

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

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 + 1];
    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 + 1];
    strcpy (s->name, n);
    //s->name = n;
}

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

int main(){

    Date date;
    date.day = 23;
    date.month = 12;
    date.year = 1993;
    Student stu;
    initialize (&stu, &date, "Zhang San");

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

    clean (&stu);

    return 0;
}

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

struct Student {
    Date birth;
    char* name;

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

 

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 + 1];
    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 + 1];
    strcpy (name, n);
}

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

int main(){

    Date date;
    date.day = 23;
    date.month = 12;
    date.year = 1993;
    Student stu;

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

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

    stu.clean ();

    return 0;
}

 

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 + 1];
    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 + 1];
    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 = 23;
    date.month = 12;
    date.year = 1993;
    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 0;
}