C ++循环依赖

Question

我遇到了循环依赖的问题，并且无法解决这个问题。

这是我在编译时收到的错误......

g++ --std=c++11 -ggdb Albums.cpp -c -o albums.o
In file included from Albums.hpp:9:0,
                 from Albums.cpp:1:
Artist.hpp:34:20: error: ‘Albums’ has not been declared
     void setAlbums(Albums *albums) { _albums = albums; }
                    ^
Artist.hpp:35:5: error: ‘Albums’ does not name a type
     Albums *albums() { return _albums; }
     ^
Artist.hpp:46:5: error: ‘Albums’ does not name a type
     Albums *_albums;
     ^
Artist.hpp: In constructor ‘Artist::Artist()’:
Artist.hpp:15:63: error: class ‘Artist’ does not have any field named ‘_albums’
             _primaryImage(nullptr), _secondaryImage(nullptr), _albums(new Albums()) {}
                                                               ^
Artist.hpp:15:75: error: expected type-specifier before ‘Albums’
             _primaryImage(nullptr), _secondaryImage(nullptr), _albums(new Albums()) {}
                                                                           ^
Artist.hpp: In member function ‘void Artist::addAlbum(Album*)’:
Artist.hpp:31:9: error: ‘_albums’ was not declared in this scope
         _albums->addAlbum(album);
         ^
Artist.hpp: In member function ‘void Artist::setAlbums(int*)’:
Artist.hpp:34:38: error: ‘_albums’ was not declared in this scope
     void setAlbums(Albums *albums) { _albums = albums; }
                                      ^
Albums.cpp: In member function ‘void Albums::setArtistForAlbums(Artists*)’:
Albums.cpp:46:32: error: invalid use of incomplete type ‘class Artists’
     for (int j = 0; j < artists->numArtists(); j++) {
                                ^
In file included from Albums.cpp:1:0:
Albums.hpp:12:7: note: forward declaration of ‘class Artists’
 class Artists;
       ^
Albums.cpp:48:33: error: invalid use of incomplete type ‘class Artists’
         Artist *artist = artists->listOfArtists()->at(i);
                                 ^
In file included from Albums.cpp:1:0:
Albums.hpp:12:7: note: forward declaration of ‘class Artists’
 class Artists;
       ^
Albums.cpp:48:55: error: ‘i’ was not declared in this scope
         Artist *artist = artists->listOfArtists()->at(i);

Artist.hpp

有一个专辑对象Albums *_albums;

艺术家无法使用转发声明，因为我需要访问某些相册功能_albums->addAlbum(album);

Albums.cpp

在这里可以看到setImagesForAlbums也需要这张专辑

void Albums::setImagesForAlbums(AlbumImages *albumImages) {
        for (int i = 0; i < albumImages->numAlbumImages(); i++) {
            Album * album = albumWithID(albumImages->listOfAlbumImages()->at(i)->albumID());
            if(album) {
                if(albumImages->listOfAlbumImages()->at(i)->type() == "primary") {
                    album->primaryImage() = albumImages->listOfAlbumImages()->at(i);
                }
                else if(albumImages->listOfAlbumImages()->at(i)->type() == "secondary") {
                    album->secondaryImage() = albumImages->listOfAlbumImages()->at(i);
            }
        }
    }
}

Albums.hpp

#ifndef __ALBUMS_HPP
#define __ALBUMS_HPP

#include <iostream>

#include "JSONArray.hpp"
#include "AlbumImages.hpp"
#include "Artist.hpp"
#include "Album.hpp"

class Artists;


class Albums: public JSONArray
{
public:
    Albums(): JSONArray() {}
    ~Albums();

    int numAlbums() { return listOfAlbums()->size(); }
    void addAlbum(Album *album);

    Album *albumWithID(unsigned int aID); // Not tested

    void loadAlbumsFromFile(std::string fileName); //
    std::string htmlString(); // Not tested
    JSONDataObject *jsonObjectNode() { return new Album();  }
    void setArtistForAlbums(Artists *artists);
    void setImagesForAlbums(AlbumImages *);
    std::vector<Album *> *listOfAlbums() { return (std::vector<Album *> *) _listOfDataObjects; }
    void runAsserts();  // used for checking the integrity of this class.

    void printAlbums();
};

#endif

Artist.hpp

#ifndef __ARTIST_HPP
#define __ARTIST_HPP

#include "JSONDataObject.hpp"
#include "ArtistImage.hpp"
#include "Albums.hpp"
// #include "Album.hpp"

// class Albums;

class Artist: public JSONDataObject {
public:
    Artist(): JSONDataObject(), _artistID(0), cachedName(false), cachedRealName(false),
            cachedProfile(false), cachedNumImages(false), cachedArtistID(false),
            _primaryImage(nullptr), _secondaryImage(nullptr), _albums(new Albums()) {}

    ~Artist();

    std::string profile();
    std::string artistName();
    std::string realName();
    std::string numImages();  // since it's a string in the JSON file
    unsigned    artistID();

    void print();
    std::string htmlString(); // Implement

    // the following 4 function-prototypes are new to this project.
    void addAlbum(Album *album) {
        // std::cout << "this in addAlbum is " << _albums << std::endl;
        _albums->addAlbum(album);
    }

    void setAlbums(Albums *albums) { _albums = albums; }
    Albums *albums() { return _albums; }
    ArtistImage *&primaryImage()       { return _primaryImage;   } // GOOD
    ArtistImage *&secondaryImage()     { return _secondaryImage; } // GOOD

private:
    std::string _name, _realName, _profile, _numImages;
    unsigned _artistID;
    bool cachedName, cachedRealName, cachedProfile, cachedNumImages, cachedArtistID;

    // the following 3 variables are new to this project.
    ArtistImage *_primaryImage, *_secondaryImage;
    Albums *_albums;
};

#endif

似乎Artist.hpp需要Albums.hpp和Albums.hpp需要Artist.hpp创建循环依赖。如何避免这种情况？