Message/Folder primer13章

#include<string>
#include<iostream>
#include<set>
class Folder; 
class Message;

class Folder
{
public:
    void delete_mess(Message* pmess) 
    {
        messages.erase(pmess);
    }
    void add_mess(Message* pmess) 
    {
        messages.insert(pmess);
    }
    ~Folder();  // 在这里定义函数会说message类没定义。要放在外面。
/*    {
        // 对于每个message 要删除指向他的folder
        for(std::set<Message*>::iterator it = messages.begin(); it != messages.end(); ++it)
            (*it)->delete_folder(this);
        std::cout << "~Folder" << std::endl;
    }*/

private:
    std::set<Message*> messages;
};


class Message
{
public:
    Message(std::string str = ""):contents(str){}
    Message(const Message& mes);
    Message& operator=(const Message& mes);
    ~Message();
    void add_folder(Folder& fo) 
        { folders.insert(&fo);fo.add_mess(this);} 
    void delete_folder(Folder* fo) 
        { folders.erase(fo); (*fo).delete_mess(this);} 
private:
    std::string contents;
    std::set<Folder*>  folders;
};


Message::Message(const Message& mes):contents(mes.contents),folders(mes.folders)
{
    
    for(std::set<Folder*>::iterator it = folders.begin(); it != folders.end(); ++it)
        (*it)->add_mess(this);
}


Message& Message::operator=(const Message& mes)
{
    if(this == &mes) return *this;
     contents = mes.contents;
    for(std::set<Folder*>::iterator it = folders.begin(); it != folders.end(); ++it)
        (*it)->delete_mess(this);

    folders = mes.folders;
    for(std::set<Folder*>::iterator it = folders.begin(); it != folders.end(); ++it)
        (*it)->add_mess(this);
    return *this;
}

Message::~Message()
{
    // 对于每一个folder要删除 每一个 folder 指向自己的信息
    for(std::set<Folder*>::iterator it = folders.begin(); it != folders.end(); ++it)
        (*it)->delete_mess(this);
    std::cout<< contents << std::endl;
}

Folder::~Folder() // 缺少析构函数会导致：如果message删除了，则Folder里面指向垃圾对象，内存报错
{
    // 对于每个message 要删除指向他的folder
    for(std::set<Message*>::iterator it = messages.begin(); it != messages.end();)
    {
        std::set<Message*>::iterator next = it;
        ++next;
        (*it)->delete_folder(this);
        it = next;        
    }
    std::cout << "~Folder" << std::endl;
}

/*Folder::~Folder()  // 这样为啥是错的。 迭代器失效的操作造成。
{
    // 对于每个message 要删除指向他的folder
    for(std::set<Message*>::iterator it = messages.begin(); it != messages.end(); ++it)
    {
        (*it)->delete_folder(this);
    }
    std::cout << "~Folder" << std::endl;
}
*/

int main()
{
    std::string s1("contents1");
    std::string s2("contents2");

    Message m1(s1);  //栈区里面定义对象的先后
    Message m2(s2);  //顺序会影响程序的执行;特别是
    Folder f1;            // Message、Folder的类定义是交叉的。
    Folder f2;   

    m2.add_folder(f2);
    m1.add_folder(f1);
    return 0;
}