第十三章 拷贝控制实例

设计一个名为Message和一个Folder的类。

体现拷贝构造函数，拷贝赋值运算符的作用。

注意：

1.两个类在实现过程中需要相互调用时，头文件的包含。

2.工具函数的使用。

//in _Folder.h#ifndef FOLDER_H#define FOLDER_H#include"_Message.h"                //*****************It's necessary************#include<iostream>#include<set>using namespace std;class Message;                          //****************It's necessary*******************class Folder            //define class Folder{    friend class Message;public:    Folder()        //default constructor    {        //empty body    }    void addMsg(Message *m);       //insert a message into this folder    void rmMsg(Message *m);        //remove a message from this folder    void display() const;        //show all messages contented in this folderprivate:    set<Message *> messages;};#endif // FOLDER_H

//in _Folder.cpp#include"_Folder.h"#include<iostream>using namespace std;void Folder::addMsg(Message *m)       //insert a message into this folder{    messages.insert(m);}void Folder::rmMsg(Message *m)        //remove a message from this folder{    messages.erase(m);}void Folder::display() const            //show all messages contented in this folder{    cout << "these message are contented in this folder:\n";    for (auto &m : messages)        m->display();}

//in _Message.h#ifndef MESSAGE_H#define MESSAGE_H#include"_Folder.h"                 //******************It's necessary***************#include<iostream>#include<string>#include<set>using namespace std;class Folder;                               //************It's necessary**********class Message{    friend class Folder;public:    Message(const string &s = string())    :contents(s)    {        //empty body    };    Message(const Message &m)          //copy constructor    :contents(m.contents), folder(m.folder)    {        add_to_folder(m);    }    Message &operator=(const Message &m);    //overload '='    ~Message();                     //destructor    void save(Folder &f);            //add this message to a folder    void remove(Folder &f);         //remove this message from a folder    void display() const;private:    string contents;    set<Folder *> folder;    void add_to_folder(const Message &m);       //utility function    void remove_from_Folder();                   //utility function};#endif // MESSAGE_H

//in _Message.cpp#include"_Message.h"#include<iostream>using namespace std;void Message::save(Folder &f)            //add this message to a folder{    folder.insert(&f);    f.addMsg(this);}void Message::remove(Folder &f)          //remove this message from a folder{    f.rmMsg(this);    folder.erase(&f);}void Message::display() const{    cout << contents << endl;}void Message::add_to_folder(const Message &m){    for (auto f : m.folder)        f->addMsg(this);}void Message::remove_from_Folder(){    for (auto f : folder)        f->rmMsg(this);}Message &Message::operator=(const Message &m){    remove_from_Folder();    contents = m.contents;    folder = m.folder;    add_to_folder(m);}Message::~Message(){    remove_from_Folder();}