c++ - 派生类序列化 - 'unregistered class' 异常

Question

试图让 boost 序列化工作。主要思想是拥有一个包含一些成员和一些派生类的基类，每个派生类都有自己的私有(private)成员以及基类成员。
这是我正在尝试做的最小版本:

class base {
    public:
        virtual void print() = 0;
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive &ar, const unsigned) {}
}

class derived20 : public base {
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive &ar, const unsigned) {
            boost::serialization::base_object<base>(*this);
            ar & var20;
        }
        
        int var20 = 20;
        
    public:
        void print() override { std::cout << var20 << std::endl; }
}

class derived40 : public base {
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive &ar, const unsigned) {
            boost::serialization::base_object<base>(*this);
            ar & var40;
        }
        
        int var40 = 40;
        
    public:
        void print() override { std::cout << var40 << std::endl; }
}

BOOST_CLASS_EXPORT(derived20)
BOOST_CLASS_EXPORT(derived40)
BOOST_CLASS_EXPORT(base)

int main(int argc, char **argv) {
    std::stringstream ss;
    
    boost::archive::text_oarchive ar(ss);
    auto d20 = new derived20();
    ar << d20;
    
    // prints:
    // 22 serialization:archive 15 0 1 0
    // 0 20
    std::cout << ss.str() << std::endl;
    
    boost::archive::text_iarchive iar(ss);
    base *b;
    iar >> b;
    b->print(); // Should print "20"
}

我收到了 archive_exception: unregistered class错误。
我到底做错了什么？

Answer 1

这是一种罕见的情况，auto可能会伤害:

auto d20 = new derived20();
ar << d20;

对比:

base *b;
iar >> b;

注意 d20是 derived20* ，而不是 base* .因此，您通过尝试反序列化包含另一种类型的存档中的类型来调用未定义的行为。
简单地改变它:

base* d20 = new derived20();

修复一切:

Also noticed that you forgot to actually serialize the base object.

Live on coliru

#include <boost/serialization/base_object.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/access.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <iostream>

class base {
    public:
        virtual void print() = 0;
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive & /*unused*/, unsigned /*unused*/) {}
};

class derived20 : public base {
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive &ar, unsigned /*unused*/) {
            ar & boost::serialization::base_object<base>(*this)
               & var20;
        }
        
        int var20 = 20;
        
    public:
        void print() override { std::cout << var20 << std::endl; }
};

class derived40 : public base {
    private:
        friend class boost::serialization::access;
        template<class Archive> void serialize(Archive &ar, const unsigned /*unused*/) {
            ar & boost::serialization::base_object<base>(*this)
               & var40;
        }
        
        int var40 = 40;
        
    public:
        void print() override { std::cout << var40 << std::endl; }
};

BOOST_CLASS_EXPORT(derived20)
BOOST_CLASS_EXPORT(derived40)
BOOST_CLASS_EXPORT(base)

int main() {
    std::stringstream ss;
    
    {
        boost::archive::text_oarchive ar(ss);
        base* d20 = new derived20();
        ar << d20;
    }
    
    // prints:
    // 22 serialization:archive 15 0 1 0
    // 0 20
    std::cout << ss.str() << std::endl;
    
    {
        boost::archive::text_iarchive iar(ss);
        base *b = nullptr;
        iar >> b;
        b->print(); // Should print "20"
    }
}

打印

22 serialization::archive 17 0 9 derived20 1 0
0 20

20