c++ - 无法归档所有数据

Question

我正在使用 boost 进行数据序列化。

这就是类的结构。

1)我有一个舞台类
此类保存导演类的 vector 数据

class Stage
{
public:
    std::vector<Director> directors;
    void AddDirector(Director dir) { directors.push_back(dir); }
    int GetDirectorSize() { return directors.size(); }
    Director* GetDirector(int number) { return &directors[number]; }

private:
    friend class boost::serialization::access;
    template<typename Archive>
    void save(Archive& ar, const unsigned int version) const {
        ar & directors;
    }
    template<typename Archive>
    void load(Archive& ar, const unsigned int version) {
        ar & directors;
    }
    BOOST_SERIALIZATION_SPLIT_MEMBER()
};

2)这是导演类
该类保存 channel 类的弱指针 vector 数据。

class Director
{
public:
    std::string stdstrName;
    std::vector<std::weak_ptr<Channel>> channels;
    Director() { stdstrName = "NO_NAME"; }
    void SetName(std::string name) { stdstrName = name; }
    std::string GetName() { return stdstrName; }
    void AddChannel(std::weak_ptr<Channel> chn) { channels.push_back(chn); }
    std::shared_ptr<Channel> GetChannel(int number) { return channels[number].lock(); }
    int GetChannelSize() {return channels.size();}
    std::string GetChannelType( int number){
        if (std::shared_ptr<Channel> chn = channels[number].lock())
            return chn->GetChannelType();   
    }

private:
    friend class boost::serialization::access;
    template<typename Archive>
    void save(Archive& ar, const unsigned int version) const {
        ar & stdstrName & channels;
    }
    template<typename Archive>
    void load(Archive& ar, const unsigned int version) {
        ar & stdstrName & channels;
    }
    BOOST_SERIALIZATION_SPLIT_MEMBER()

};

3)这是 channel 类

Channel 类需要知道创建它的容器和
将其存储为 Weak_pointer 的主管

1) 这个类拥有一个指向 Director 对象的指针。

2) 这个类持有一个指向 Container 对象的指针。

class Container;
class Director;

class Channel
{
public:
    Director* dir;
    Container* cont;
    std::string stdstrChannelType;
    Channel() { stdstrChannelType = "NO_TYPE"; }
    Channel(std::string type): stdstrChannelType(type){  }
    void SetDirector(Director* director);
    void SetContainer(Container* container);
    std::string GetChannelType() { return  stdstrChannelType;}
    Director* GetDirector() { return dir; }

private:
    friend class boost::serialization::access;
    template<typename Archive>
    void save(Archive& ar, const unsigned int version) const {
        ar & dir & cont & stdstrChannelType;
    }
    template<typename Archive>
    void load(Archive& ar, const unsigned int version) {
        ar & dir & cont & stdstrChannelType;
    }
    BOOST_SERIALIZATION_SPLIT_MEMBER()

};

///////////////////////////////////////////////////////////////////////

 #include "Channel.h"
#include <vector>

class PositionChannel : public Channel
{
public:
    std::vector<int> keyframes;
    PositionChannel() : Channel("POSITION") , keyframes( { 1 , 2, 3 }) {    }

   private:
   friend class boost::serialization::access;

typedef Channel _Super;
template<typename Archive>
void save(Archive& ar, const unsigned int version) const {
    ar & boost::serialization::base_object<_Super>(*this);
    ar & keyframes;
}
template<typename Archive>
void load(Archive& ar, const unsigned int version) {
    ar & keyframes;
}
BOOST_SERIALIZATION_SPLIT_MEMBER()

};

4)这是容器类

1) 这是创建 Channel 并保存为 Shared_pointer 的地方。

2)同样的 channel 也作为Weak_Pointer保存在Director类中

class Container
{
public:
    std::string stdstrName;
    std::vector<std::shared_ptr<Channel>> channel;
    Container() { stdstrName = "cont"; };
    void AddChannel(std::shared_ptr<Channel> chn) 
    { 
        channel.push_back(chn); 
        Director* dir = chn->GetDirector();  // Add the channel to director also
        dir->AddChannel(chn);
    }

private:
    friend class boost::serialization::access;
    template<typename Archive>
    void save(Archive& ar, const unsigned int version) const {
        ar & stdstrName & channel;
    }
    template<typename Archive>
    void load(Archive& ar, const unsigned int version) {
        ar & stdstrName & channel;
    }
    BOOST_SERIALIZATION_SPLIT_MEMBER()

};

现在，当我序列化我的数据而不是序列化它时，Director 无法序列化weak_pointer。

Stage stage;
Director dir;
Container cont;
dir.SetName("MAIN");
stage.AddDirector(dir); // Add director to stage
std::shared_ptr<PositionChannel> chn = std::make_shared<PositionChannel>(PositionChannel()); // create a position channel
chn->SetDirector(&dir); // Link the director to channel
chn->SetContainer(&cont); // Link the container to the channel
cont.AddChannel(chn);   // add the channel to the container
std::cout << dir.GetChannelSize() << std::endl; // this gives a value of 1 which is correct
std::ofstream ofs("D://abc.dat");
{
    boost::archive::text_oarchive oa(ofs);
    // write class instance to archive
    oa << stage <<  cont;  // since director is a data element of stage so it should get serialized
}
Stage stage1;
Container cont1;
{
    // create and open an archive for input
    std::ifstream ifs("D://abc.dat");
    boost::archive::text_iarchive ia(ifs);
    // read class state from archive
    ia >> stage1 >> cont1;

}
std::cout << stage1.GetDirectorSize(); // stage has got the director
Director* dir1 = stage1.GetDirector(0);
std::cout << dir1->GetName(); // the director has the correct name
std::cout << dir1->GetChannelSize(); // it should show 1 as the channel size but i am getting 0

Answer 1

当你这样做

stage.AddDirector(dir); // Add director to stage

它增加了 一份的 dir到 stage::directors` vector 。

以后你做

chn->SetDirector(&dir); // Link the director to channel

这意味着您将变量指向 main .这与被推上舞台的人不同。这可能不是您想要的。

比较:

chn->cont = &cont;

设置指向 cont 的指针，即 还有只是 main 范围内的一个变量.最大的区别在于该确切的对象被序列化到存档中，因此如果存档找到指向它的指针，它可以正确地建立链接。

指针冲突

当一个对象第一次通过指针反序列化时，它不能再通过引用反序列化(因为指向的对象已经被动态分配)。

查看更多背景信息: http://www.bnikolic.co.uk/blog/cpp-boost-ser-conflict.html

在您的情况下，您有如此多的循环依赖关系，没有顺序可以序列化 stage和 cont所以它不会导致指针冲突。

解决问题的最简单方法是使 vector<Director>进入 vector<shared_ptr<Director> > .那你还是要确定 cont在 stage 之前被序列化.

固定演示

这是一个有效的简化演示:

Live On Coliru

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/vector.hpp>
#include <boost/serialization/base_object.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/serialization/weak_ptr.hpp>
#include <boost/serialization/export.hpp>
#include <fstream>

namespace Lib {
    struct Container;
    struct Director;

    struct Channel {
        Director* dir = nullptr;
        Container* cont = nullptr;
        virtual ~Channel() = default;
    };
    struct PositionChannel : Channel {
        std::vector<int> keyframes;
    };
    struct Director {
        std::string name;
        std::vector<std::weak_ptr<Channel>> channels;
    };
    struct Stage {
        std::vector<std::shared_ptr<Director> > directors;
    };
    struct Container {
        std::vector<std::shared_ptr<Channel> > channels;
    };

    template <typename Ar> void serialize(Ar& ar, Channel& o, unsigned) {
        //ar & o.dir & o.cont; // avoid pointer conflict
        ar & o.cont & o.dir;
    }
    template <typename Ar> void serialize(Ar& ar, PositionChannel& o, unsigned) {
        ar & boost::serialization::base_object<Channel>(o)
           & o.keyframes;
    }
    template <typename Ar> void serialize(Ar& ar, Director& o, unsigned) {
        ar & o.name & o.channels;
    }
    template <typename Ar> void serialize(Ar& ar, Stage& o, unsigned) {
        ar & o.directors;
    }
    template <typename Ar> void serialize(Ar& ar, Container& o, unsigned) {
        ar & o.channels;
    }
}

BOOST_CLASS_EXPORT(Lib::Channel)
BOOST_CLASS_EXPORT(Lib::PositionChannel)

int main() {
    using namespace Lib;
    {
        Stage stage;
        Container cont;

        auto dir = std::make_shared<Director>();
        dir->name = "MAIN";
        stage.directors.push_back(dir); // Add director to stage

        auto chn = std::make_shared<PositionChannel>(PositionChannel()); // create a position channel
        chn->dir = dir.get();
        chn->cont = &cont;

        dir->channels.emplace_back(chn); // add the weak ptr

        cont.channels.insert(cont.channels.end(),
            { 
                chn,
                std::make_shared<PositionChannel>(),
                std::make_shared<PositionChannel>(),
                std::make_shared<PositionChannel>(),
            });

        {
            std::ofstream ofs("abc.dat");
            boost::archive::text_oarchive oa(ofs);
            //oa << stage << cont;
            oa << cont << stage;
        }
    }

    {
        std::ifstream ifs("abc.dat");
        boost::archive::text_iarchive ia(ifs);
        Stage stage;
        Container cont;

        //ia >> stage >> cont;
        ia >> cont >> stage;

        assert(cont.channels.size() == 4);

        auto chn = cont.channels.front();
        assert(chn == chn->dir->channels.front().lock());
        assert(chn->cont == &cont);
    }
}

它通过所有断言并写入一个文本存档，其中包含:

22 serialization::archive 17 1 0
0 0 0 4 1 0 1 4 20 Lib::PositionChannel 1 0
1 1 0
2 0 0 5 1 0
3 4 MAIN 0 0 1 0 0 0 4 1 0 0 4
4
5 -1 -1 0 0 4
6
7 -1 -1 0 0 4
8
9 -1 -1 0 0 0 0 0 0 1 1 0 1 5 3