C++ 提升引用成员抽象类的序列化

我试图弄清楚如何序列化我与Boost组合在一起的类。我将直接进入代码：

#ifndef TEST_H_
#define TEST_H_

#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>

class Parent
{
public:
        int test_val = 1234234;
        int p()
        {
                return 13294;
        }
        int get_test_val()
        {
                std::cout << test_val << std::endl;
                return test_val;
        }
        friend class boost::serialization::access;
        template<class Archive>
            void serialize(Archive &ar, const unsigned int /*version*/)
        {
                ar &test_val;
        }
};

class RefMem : public Parent
{
public: 
        RefMem()
        {
                test_val = 12342;
                std::cout << test_val << std::endl;
        }
};


class Test
{
public:
        friend class boost::serialization::access;
        int t_;
        Parent &parent_;
        Test(int t, Parent &&parent = RefMem());
        template<class Archive>
        void serialize(Archive &ar, const unsigned int file_version){
                ar &t_;
                ar &parent_;
        }
        //template<class
};


#endif

\ifndef测试_
#定义测试_
#包括
#包括
#包括
#包括
班级家长
{
公众：
int test_val=1234234；
int p（）
{
返回13294；
}
int get_test_val（）
{
std：：cout您对引用的所有权语义感到困惑

引用
parent \
仅“指向”一个
RefMem
的实例。当您序列化时，编写这些引用“很容易”（因为它们是左值引用，值本身将被序列化）

然而，对于反序列化，事情并不是那么简单，因为我们没有指向的
MemRef
实例凭空动态实例化一个
MemRef
，并静默地将引用点指向它。但是，这最多会导致内存泄漏

引用成员还有一点特别重要，引用成员只能在构造函数的初始值设定项列表中初始化

因为Boost序列化序列化了值，所以它不会构造这些对象，问题是引用如何初始化

您当前的构造函数存在许多相关问题：

Test(int t, Parent && parent = RefMem()) : parent_(parent) {
    std::cout << __FUNCTION__ << ":" << this->parent_.test_val << "\n";
    t_      = t;
    parent_ = parent; // OOPS! TODO FIXME
}

与您认为的不同。它将
父对象的值从
父对象复制到
父对象
引用的对象上。这可能不可见，因为
父对象
和
父对象
在这里是同一个对象，但甚至涉及到对象切片（）



你怎么办？
最好重新组合并点击文档：

包含引用成员的类通常需要非默认值
构造函数作为引用只能在构造实例时设置。
如果类具有
引用成员。这就提出了一个问题，即对象如何以及在哪里
被引用的内容被存储，以及它们是如何创建的。还有
关于多态基类的引用的问题。基本上，这些是
关于指针也会出现同样的问题，这一点也不奇怪
引用实际上是一种特殊的指针

我们通过序列化引用来解决这些问题，就好像它们是
指针。

（强调矿山）

文档确实建议
加载构造数据
/
保存构造数据
，以减轻
测试
的非默认构造性

请注意，他们建议将引用成员作为指针处理，这似乎不错，但只有当实际指向的对象也通过同一个存档中的指针进行序列化时，才有意义。在这种情况下，将发现别名指针并避免创建重复实例

如果没有，您仍然会有内存泄漏，并且可能会破坏程序状态

使用
加载/保存构造数据的演示
这里是上述技术的一个演示。请注意，我们正在泄漏动态分配的对象。我不喜欢这种样式，因为它本质上将引用视为指针

如果这是我们想要的，我们应该考虑使用指针（见下文）

#ifndef TEST_H_
#define TEST_H_

#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>

class Parent {
  public:
    int test_val = 1234234;

    int p() { return 13294; }

    int get_test_val() {
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
        return test_val;
    }

    template <class Archive> void serialize(Archive &ar, unsigned) {
        ar & test_val; 
    }
};

class RefMem : public Parent {
  public:
    RefMem() {
        test_val = 12342;
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
    }
};

class Test {
  public:
    friend class boost::serialization::access;
    int t_;
    Parent &parent_;

    Test(int t, Parent& parent) : parent_(parent) {
        std::cout << __PRETTY_FUNCTION__ << ":" << this->parent_.test_val << "\n";
        t_      = t;
    }

    template <class Archive> void serialize(Archive &ar, const unsigned int file_version) {
        ar &t_;
        //ar &parent_; // how would this behave? We don't own it... Use pointers
    }
    // template<class
};

namespace boost { namespace serialization {
    template<class Archive>
        inline void save_construct_data(Archive & ar, const Test * t, const unsigned int file_version) {
            // save data required to construct instance
            ar << t->t_;
            // serialize reference to Parent as a pointer
            Parent* pparent = &t->parent_;
            ar << pparent;
        }

    template<class Archive>
        inline void load_construct_data(Archive & ar, Test * t, const unsigned int file_version) {
            // retrieve data from archive required to construct new instance
            int m;
            ar >> m;
            // create and load data through pointer to Parent
            // tracking handles issues of duplicates.
            Parent * pparent;
            ar >> pparent;
            // invoke inplace constructor to initialize instance of Test
            ::new(t)Test(m, *pparent);
        }
}}

#endif

#include <iostream>
#include <sstream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

int main() {
    Parent* the_instance = new RefMem;

    Test test = Test(50, *the_instance);

    std::cout << "t_: " << test.t_ << "\n";
    std::cout << "Test val: " << test.parent_.get_test_val() << "\n";
    std::ostringstream oss;
    {
        boost::archive::text_oarchive oa(oss);
        Test* p = &test;
        oa << the_instance << p; // NOTE SERIALIZE test AS-IF A POINTER
    }

    {
        Parent* the_cloned_instance = nullptr;
        Test* cloned = nullptr;

        std::istringstream iss(oss.str());
        {
            boost::archive::text_iarchive ia(iss);
            ia >> the_cloned_instance >> cloned;
        }

        std::cout << "t_: " << cloned->t_ << "\n";
        std::cout << "Test val: " << cloned->parent_.get_test_val() << "\n";
        std::cout << "Are Parent objects aliasing: " << std::boolalpha << 
            (&cloned->parent_ == the_cloned_instance) << "\n";
    }
}

#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/make_shared.hpp>

class Parent {
  public:
    int test_val = 1234234;

    int p() { return 13294; }

    int get_test_val() {
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
        return test_val;
    }

    template <class Archive> void serialize(Archive &ar, unsigned) {
        ar & test_val; 
    }
};

class RefMem : public Parent {
  public:
    RefMem() {
        test_val = 12342;
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
    }
};

using ParentRef = boost::shared_ptr<Parent>;

class Test {
  public:
    int t_ = 0;
    ParentRef parent_;

    Test() = default;
    Test(int t, ParentRef parent) : t_(t), parent_(parent) { }

    template <class Archive> void serialize(Archive &ar, const unsigned int file_version) {
        ar & t_ & parent_;
    }
};

#include <sstream>

int main() {
    ParentRef the_instance = boost::make_shared<RefMem>();

    Test test = Test(50, the_instance);

    std::cout << "t_: " << test.t_ << "\n";
    std::cout << "Test val: " << test.parent_->get_test_val() << "\n";
    std::ostringstream oss;
    {
        boost::archive::text_oarchive oa(oss);
        oa << the_instance << test; // NOTE SERIALIZE test AS-IF A POINTER
    }

    {
        ParentRef the_cloned_instance;
        Test cloned;

        std::istringstream iss(oss.str());
        {
            boost::archive::text_iarchive ia(iss);
            ia >> the_cloned_instance >> cloned;
        }

        std::cout << "t_: " << cloned.t_ << "\n";
        std::cout << "Test val: " << cloned.parent_->get_test_val() << "\n";
        std::cout << "Are Parent objects aliasing: " << std::boolalpha << 
            (cloned.parent_ == the_cloned_instance) << "\n";
    }
}

或者：说出我们想要的
为了避免与引用成员相关的泄漏和可用性问题，让我们改用共享的\u ptr


#ifndef TEST_H_
#define TEST_H_

#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>

class Parent {
  public:
    int test_val = 1234234;

    int p() { return 13294; }

    int get_test_val() {
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
        return test_val;
    }

    template <class Archive> void serialize(Archive &ar, unsigned) {
        ar & test_val; 
    }
};

class RefMem : public Parent {
  public:
    RefMem() {
        test_val = 12342;
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
    }
};

class Test {
  public:
    friend class boost::serialization::access;
    int t_;
    Parent &parent_;

    Test(int t, Parent& parent) : parent_(parent) {
        std::cout << __PRETTY_FUNCTION__ << ":" << this->parent_.test_val << "\n";
        t_      = t;
    }

    template <class Archive> void serialize(Archive &ar, const unsigned int file_version) {
        ar &t_;
        //ar &parent_; // how would this behave? We don't own it... Use pointers
    }
    // template<class
};

namespace boost { namespace serialization {
    template<class Archive>
        inline void save_construct_data(Archive & ar, const Test * t, const unsigned int file_version) {
            // save data required to construct instance
            ar << t->t_;
            // serialize reference to Parent as a pointer
            Parent* pparent = &t->parent_;
            ar << pparent;
        }

    template<class Archive>
        inline void load_construct_data(Archive & ar, Test * t, const unsigned int file_version) {
            // retrieve data from archive required to construct new instance
            int m;
            ar >> m;
            // create and load data through pointer to Parent
            // tracking handles issues of duplicates.
            Parent * pparent;
            ar >> pparent;
            // invoke inplace constructor to initialize instance of Test
            ::new(t)Test(m, *pparent);
        }
}}

#endif

#include <iostream>
#include <sstream>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>

int main() {
    Parent* the_instance = new RefMem;

    Test test = Test(50, *the_instance);

    std::cout << "t_: " << test.t_ << "\n";
    std::cout << "Test val: " << test.parent_.get_test_val() << "\n";
    std::ostringstream oss;
    {
        boost::archive::text_oarchive oa(oss);
        Test* p = &test;
        oa << the_instance << p; // NOTE SERIALIZE test AS-IF A POINTER
    }

    {
        Parent* the_cloned_instance = nullptr;
        Test* cloned = nullptr;

        std::istringstream iss(oss.str());
        {
            boost::archive::text_iarchive ia(iss);
            ia >> the_cloned_instance >> cloned;
        }

        std::cout << "t_: " << cloned->t_ << "\n";
        std::cout << "Test val: " << cloned->parent_.get_test_val() << "\n";
        std::cout << "Are Parent objects aliasing: " << std::boolalpha << 
            (&cloned->parent_ == the_cloned_instance) << "\n";
    }
}

#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/make_shared.hpp>

class Parent {
  public:
    int test_val = 1234234;

    int p() { return 13294; }

    int get_test_val() {
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
        return test_val;
    }

    template <class Archive> void serialize(Archive &ar, unsigned) {
        ar & test_val; 
    }
};

class RefMem : public Parent {
  public:
    RefMem() {
        test_val = 12342;
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
    }
};

using ParentRef = boost::shared_ptr<Parent>;

class Test {
  public:
    int t_ = 0;
    ParentRef parent_;

    Test() = default;
    Test(int t, ParentRef parent) : t_(t), parent_(parent) { }

    template <class Archive> void serialize(Archive &ar, const unsigned int file_version) {
        ar & t_ & parent_;
    }
};

#include <sstream>

int main() {
    ParentRef the_instance = boost::make_shared<RefMem>();

    Test test = Test(50, the_instance);

    std::cout << "t_: " << test.t_ << "\n";
    std::cout << "Test val: " << test.parent_->get_test_val() << "\n";
    std::ostringstream oss;
    {
        boost::archive::text_oarchive oa(oss);
        oa << the_instance << test; // NOTE SERIALIZE test AS-IF A POINTER
    }

    {
        ParentRef the_cloned_instance;
        Test cloned;

        std::istringstream iss(oss.str());
        {
            boost::archive::text_iarchive ia(iss);
            ia >> the_cloned_instance >> cloned;
        }

        std::cout << "t_: " << cloned.t_ << "\n";
        std::cout << "Test val: " << cloned.parent_->get_test_val() << "\n";
        std::cout << "Are Parent objects aliasing: " << std::boolalpha << 
            (cloned.parent_ == the_cloned_instance) << "\n";
    }
}

#包括
#包括
#包括
#包括
#包括
#包括
班级家长{
公众：
int test_val=1234234；
int p（）{return 13294；}
int get_test_val（）{
std：：cout添加了两个活样本，两个都添加了一个，避免了所有的陷阱。答案很好。我将不得不读几遍。我使用双安培的原因之一是来自这里的一个建议：…是否有一个干净的（无泄漏）根据您在此处所做的操作，将默认值的功能获取到抽象参数的方法？我注意到您忽略了它。关于
父项&&
：很好的观点。我对他的回答发表了评论，他在那里犯了一个错误。关于默认值：我没有忽略它。没有抽象参数这样的东西。（您可能指的是对多态基的引用）。在我的“理智方法”中，默认值只是一个空的共享_指针，但请随意给它一个默认值，因为智能指针将进行清理。这是一个非常好用的方法。因此有多个答案，文档中也有：
#include <iostream>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/make_shared.hpp>

class Parent {
  public:
    int test_val = 1234234;

    int p() { return 13294; }

    int get_test_val() {
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
        return test_val;
    }

    template <class Archive> void serialize(Archive &ar, unsigned) {
        ar & test_val; 
    }
};

class RefMem : public Parent {
  public:
    RefMem() {
        test_val = 12342;
        std::cout << __PRETTY_FUNCTION__ << ":" << test_val << "\n";
    }
};

using ParentRef = boost::shared_ptr<Parent>;

class Test {
  public:
    int t_ = 0;
    ParentRef parent_;

    Test() = default;
    Test(int t, ParentRef parent) : t_(t), parent_(parent) { }

    template <class Archive> void serialize(Archive &ar, const unsigned int file_version) {
        ar & t_ & parent_;
    }
};

#include <sstream>

int main() {
    ParentRef the_instance = boost::make_shared<RefMem>();

    Test test = Test(50, the_instance);

    std::cout << "t_: " << test.t_ << "\n";
    std::cout << "Test val: " << test.parent_->get_test_val() << "\n";
    std::ostringstream oss;
    {
        boost::archive::text_oarchive oa(oss);
        oa << the_instance << test; // NOTE SERIALIZE test AS-IF A POINTER
    }

    {
        ParentRef the_cloned_instance;
        Test cloned;

        std::istringstream iss(oss.str());
        {
            boost::archive::text_iarchive ia(iss);
            ia >> the_cloned_instance >> cloned;
        }

        std::cout << "t_: " << cloned.t_ << "\n";
        std::cout << "Test val: " << cloned.parent_->get_test_val() << "\n";
        std::cout << "Are Parent objects aliasing: " << std::boolalpha << 
            (cloned.parent_ == the_cloned_instance) << "\n";
    }
}