当我将该类放在另一个类的地图中时，类字符串变量会丢失其值

Question

问题是，当我将这些类放在TransparentMaze类的地图中时，我的会议室类会丢失其字符串变量“name”值。我无法理解他们去哪里..问题是与地图比较器有什么关系，希望有人可以提供帮助。

#include <iostream>
#include <string>
#include <list>
#include <map>

using namespace std;

class Point{
    int x;
    int y;
    public:
        Point(int, int);
        ~Point(){};
        int getX() ;
        int getY() ;
};

struct cmp_str {
    bool operator()(Point p1, Point p2) {
        if (p1.getY() < p2.getY() || p1.getY() == p2.getY() && p1.getX() < p2.getX()) {
            return true;
        }
        return false;
    }
};

class Room{
    Room *north;
    Room *south;
    Room *east;
    Room *west;
    public:
        int createDirection[4];
        std::string name;
        Room(std::string);
        ~Room();
        std::string getName();
        std::list<std::string> findPathTo(std::string);
        void fillMap(map<Point, Room*, cmp_str>*, int*, int*);
        Room& createNorth(std::string);
        Room& createSouth(std::string);
        Room& createEast(std::string);
        Room& createWest(std::string);
        Room& getNorth();
        Room& getSouth();
        Room& getEast();
        Room& getWest();
        Room& get(std::string);
        Room& get(std::list<std::string>);
        void setNorth(Room*);
        void setSouth(Room*);
        void setEast(Room*);
        void setWest(Room*);
        //bool validatePath(std::list<std::string>);
};

class Maze{
    Room *entry;
    public:
        Maze(string);
        ~Maze();
        Room& getEntry();
};

class TransparentMaze{
    std::map<Point, Room*, cmp_str> maze;
    int width;
    int height;
    public:
        TransparentMaze(Maze);
        ~TransparentMaze(){};
        std::map<Point, Room*, cmp_str>& getMaze();
};

TransparentMaze::TransparentMaze(Maze maze) {
    maze.getEntry().fillMap(&this->maze, &this->width, &this->height);
}

std::map<Point, Room*, cmp_str>& TransparentMaze::getMaze() {
    return maze;
}

Point::Point(int x, int y) {
    this->x = x;
    this->y = y;
}

int Point::getX() {
    return x;
}

int Point::getY() {
    return y;
}

Maze::Maze(std::string name) {
    entry = new Room(name);
}

Maze::~Maze() {
    delete entry;
}

Room& Maze::getEntry() {
    return *entry;
}

Room::Room(std::string name) {
    this->name = name;
    for (int i = 0; i < sizeof(createDirection) / sizeof(int); i++) {
        createDirection[i] = 0;
    }
    north = NULL;
    south = NULL;
    east = NULL;
    west = NULL;
}

Room::~Room() {
    for (int i = 0; i < sizeof(createDirection) / sizeof(int); i++) {
        switch(i) {
            case 0:
                if (createDirection[i] == 1) {
                    delete north;
                }
                break;
            case 1:
                if (createDirection[i] == 1) {
                    delete south;
                }
                break;
            case 2:
                if (createDirection[i] == 1) {
                    delete east;
                }
                break;
            case 3:
                if (createDirection[i] == 1) {
                    delete west;
                }
                break;
        }
    }
}

Room& Room::get(std::string direction) {
    switch(direction[0]) {  
        case 'N': case 'n': return (this->north == NULL ? *this : *this->north);
        case 'S': case 's': return (this->south == NULL ? *this : *this->south);
        case 'E': case 'e': return (this->east == NULL ? *this : *this->east);
        case 'W': case 'w': return (this->west == NULL ? *this : *this->west);
        default: break;
    }
    return *this;
}

Room& Room::get(std::list<std::string> pathList) {
    std::list<std::string>::iterator it;
    Room *room = this;

    for (it = pathList.begin(); it != pathList.end(); it++) {
        if (&(*room) == &room->get(*it)) {
            return *this;
        }
        room = &room->get(*it);
    }
    return *room;
}

void Room::fillMap(map<Point, Room*, cmp_str> *maze, int *width, int *height) {
    std::list<std::list<std::string>> listOfLists;
    std::list<std::list<std::string>>::iterator it1;
    Room *r;
    int n, counter;

    *width = *height = 0;
    listOfLists.push_back(std::list<std::string>());
    for (;;) {

        counter = 0;
        for (it1 = listOfLists.begin(); it1 != listOfLists.end(); it1++) {
            r = &this->get(*it1);

            //Point p((int)r->getName()[0] - 64, (int)r->getName()[1] - 48);
            //cout << r->getName() << " " << &*r << "  " << &this->get(*it1) << endl;
            maze->insert(std::make_pair(Point((int)r->getName()[0] - 64, (int)r->getName()[1] - 48), &*r));
            //cout << r->getName() << endl;
            std::string lastRoom;
            n = 0;

            if (it1->size() > 0) {
                lastRoom = *--it1->end();
            }
            if (&r->getNorth() != NULL && lastRoom.compare("S") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("N");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("N");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getEast() != NULL && lastRoom.compare("W") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("E");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("E");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getWest() != NULL && lastRoom.compare("E") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("W");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("W");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getSouth() != NULL && lastRoom.compare("N") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("S");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("S");
                    listOfLists.push_back(bufferList);
                }
            }
        }

        if(counter == 0) {
            /*cout << listOfLists.size() << endl;
            map<Point, Room*, cmp_str>::iterator it;
            for (it = maze->begin(); it != maze->end(); it++) {
                cout << "X: "<< it->first.getX() << " Y: " << it->first.getY() << "; " << (*it->second).getName() << endl;
            }*/
            return;
        }
    }
}

std::list<std::string> Room::findPathTo(std::string roomName) {
    std::list<std::list<std::string>> listOfLists;
    std::list<std::list<std::string>>::iterator it1;
    Room *r;
    int n, counter;

    listOfLists.push_back(std::list<std::string>());
    for (;;) {

        counter = 0;
        for (it1 = listOfLists.begin(); it1 != listOfLists.end(); it1++) {
            r = &this->get(*it1);
            std::string lastRoom;
            n = 0;

            if (it1->size() > 0) {
                lastRoom = *--it1->end();
            }
            if (r->getName().compare(roomName) == 0) {

                return *it1;
            }
            if (&r->getNorth() != NULL && lastRoom.compare("S") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("N");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("N");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getEast() != NULL && lastRoom.compare("W") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("E");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("E");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getWest() != NULL && lastRoom.compare("E") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("W");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("W");
                    listOfLists.push_back(bufferList);
                }
            }
            if (&r->getSouth() != NULL && lastRoom.compare("N") != 0) {
                n++;
                counter++;
                if (n == 1) {
                    it1->push_back("S");
                }  else {
                    std::list<std::string> bufferList(it1->begin(), --it1->end());
                    bufferList.push_back("S");
                    listOfLists.push_back(bufferList);
                }
            }
        }

        if(counter == 0) {
            return std::list<std::string>();
        }
    }
}

/*bool Room::validatePath(std::list<std::string> pathList) {
    std::list<std::string>::iterator it;
    Room *room = this;

    for (it = pathList.begin(); it != pathList.end(); it++) {
        if (&(*room) == &room->get(*it)) {
            return false;
        }
        room = &room->get(*it);
    }
    return true;
}*/

std::string Room::getName(){
    return name;
}

Room& Room::createNorth(std::string name) {
    north = new Room(name);
    createDirection[0] = 1;
    north->setSouth(this);
    return *north;
}

Room& Room::createSouth(std::string name) {
    south = new Room(name);
    createDirection[1] = 1;
    south->setNorth(this);
    return *south;
}

Room& Room::createEast(std::string name) {
    east = new Room(name);
    createDirection[2] = 1;
    east->setWest(this);
    return *east;
}

Room& Room::createWest(std::string name) {
    west = new Room(name);
    createDirection[3] = 1;
    west->setEast(this);
    return *west;
}

Room& Room::getNorth() {
    return *north;
}

Room& Room::getSouth() {
    return *south;
}

Room& Room::getEast() {
    return *east;
}

Room& Room::getWest() {
    return *west;
}

void Room::setNorth(Room *room) {
    north = room;
}

void Room::setSouth(Room *room) {
    south = room;
}

void Room::setEast(Room *room) {
    east = room;
}

void Room::setWest(Room *room) {
    west = room;
}

int main() {
    Maze maze("A5");

    maze.getEntry().createSouth("A6").createEast("B6").createSouth("B7").createWest("A7")
        .getEast().createEast("C7").createNorth("C6").createEast("D6").createEast("E6")
        .getWest().createNorth("D5").createEast("E5").getWest().getSouth().getWest()
        .createNorth("C5").createWest("B5").createNorth("B4").createWest("A4").createNorth("A3")
        .getSouth().getEast().getSouth().getEast().createNorth("C4").createNorth("C3")
        .createWest("B3").getEast().createNorth("C2").createWest("B2").createWest("A2")
        .createNorth("A1").getSouth().getEast().getEast().createEast("D2").createSouth("D3")
        .createSouth("D4").createEast("E4").createNorth("E3").createNorth("E2").createNorth("E1")
        .createWest("D1").createWest("C1").createWest("B1").getEast().getEast().getEast()
        .createEast("F1").createEast("G1").createEast("H1").createSouth("H2").createEast("I2")
        .createSouth("I3").createEast("J3").createNorth("J2").createNorth("J1").createWest("I1")
        .getEast().getSouth().getSouth().getWest().getNorth().getWest().getNorth().getWest()
        .getWest().getWest().getSouth().getSouth().createEast("F3").createEast("G3")
        .createNorth("G2").createWest("F2").getEast().getSouth().createEast("H3").createSouth("H4")
        .createEast("I4").createEast("J4").createSouth("J5").createWest("I5").createWest("H5")
        .getEast().createSouth("I6").createEast("J6").createSouth("J7").createWest("I7")
        .createWest("H7").createWest("G7").getEast().createNorth("H6").createWest("G6")
        .createWest("F6").createNorth("F5").createNorth("F4").createEast("G4").createSouth("G5")
        .getNorth().getWest().getSouth().getSouth().createSouth("F7").createWest("E7")
        .createWest("D7");

    //cout << (int)'A' << endl;
    //cout << (int)'1' << endl;

    /*std::list<std::string> list(maze.getEntry().findPathTo("E7"));
    std::list<std::string>::iterator it;

    for (it = list.begin(); it != list.end(); it++) {
        cout << *it << endl;
    }*/

    //cout << sizeof(maze.getEntry()) << endl;



    //Here it has still a value..
    cout << maze.getEntry().getName().length() << endl;
    TransparentMaze tMaze(maze);
    //Here not anymore.. why it's gone?
    cout << maze.getEntry().getName().length() << endl;




    //tMaze.getMaze();
    /*map<Point, Room*, cmp_str>::iterator it;
    for (it = tMaze.getMaze().begin(); it != tMaze.getMaze().end(); it++) {
        cout << "X: "<< it->first.getX() << " Y: " << it->first.getY() << "; " << it->second->name << endl;
    }*/


}

Answer 1

这有点复杂，但这是正在发生的事情。简而言之，TransparentMaze构造函数获取按值传递的Maze实例，但Maze类不能安全复制（它包含指针）。解决此问题的最简单方法是将Maze设置为不可复制（下方更多），并使TransparentMaze引用Maze（Maze&）而不是副本。

class Maze{
    Room *entry;

    // these two lines make it non-copyable
    Maze(const Maze&);            // <-- private copy constructor
    Maze& operator=(const Maze&); // <-- private assignment operator

    public:
        Maze(string);
        ~Maze();
        Room& getEntry();
};


class TransparentMaze{
    std::map<Point, Room*, cmp_str> maze;
    int width;
    int height;
    public:
        TransparentMaze(Maze&);  // pass by reference
        ~TransparentMaze(){};
        std::map<Point, Room*, cmp_str>& getMaze();
};

TransparentMaze::TransparentMaze(Maze& maze) {
    maze.getEntry().fillMap(&this->maze, &this->width, &this->height);
}

构造TransparentMaze时，构造函数获取Maze的副本，该副本生成entry指针的副本。当TransparentMaze构造函数完成并且~Maze析构函数删除entry指针时，将删除此副本。当您稍后尝试使用已删除的entry指针时（在原始maze实例中复制它），您将得到未定义的行为（我的系统崩溃了）。

Answer 2

这是很多代码。它有很多问题，但你遇到的实际问题是 - 你的对象执行浅拷贝，并在破坏时自行清理。以这种方式使用的浅副本将无法正常工作，因为当一个副本被销毁时，将释放对象的后续副本中指向的内存 - 在其余对象中留下悬空指针。

// This function takes a COPY of the Maze object
TransparentMaze::TransparentMaze(Maze maze)

// But the Maze object cannot be safely copied
// because it only does a shallow copy
// and destroy's its entry upon destruction
Maze::~Maze() {
   delete entry;
}

考虑将Maze和Room中的原始指针移动到智能指针类型，或者您必须为所有类编写copy-constructors。

有关深拷贝与浅拷贝的讨论，请参阅this question。