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serialize and deserialize a class in cpp

Guide

how to serialize string

size + data

The easiest serialization method for strings or other blobs with variable size is to serialize first the size as you serialize integers, then just copy the content to the output stream.
When reading you first read the size, then allocate the string and then fill it by reading the correct number of bytes from the stream.

with ostream/istream

native way with ostream/istream for example class MyClass with height,width,name fields.

class MyClass {
public:
    int height;
   int width;
   std::string name;
}

std::ostream& MyClass::serialize(std::ostream &out) const {
    out << height;
    out << ',' //number seperator
    out << width;
    out << ',' //number seperator
    out << name.size(); //serialize size of string
    out << ',' //number seperator
    out << name; //serialize characters of string
    return out;
}
std::istream& MyClass::deserialize(std::istream &in) {
    if (in) {
        int len=0;
        char comma;
        in >> height;
        in >> comma; //read in the seperator
        in >> width;
        in >> comma; //read in the seperator
        in >> len;  //deserialize size of string
        in >> comma; //read in the seperator
        if (in && len) {
            std::vector<char> tmp(len);
            in.read(tmp.data() , len); //deserialize characters of string
            name.assign(tmp.data(), len);
        }
    }
    return in;
}

overload for operator<< and operator>>

std::ostream& operator<<(std::ostream& out, const MyClass &obj)
{
    obj.serialize(out); 
    return out;
}

std::istream& operator>>(std::istream& in, MyClass &obj)
{
    obj.deserialize(in); 
    return in;
}

with boost serialization

archive file format

text: text_iarchive,text_oarchive field
xml: xml_iarchive,xml_oarchive, with BOOST_SERIALIZATION_NVP(field)
binary: binary_iarchive,binary_oarchive with stringstream or fstream.

text archive

change BOOST_SERIALIZATION_NVP(field) to field

xml archive

#include <boost/archive/text_iarchive.hpp> 
#include <boost/archive/text_oarchive.hpp> 
#include <boost/archive/xml_iarchive.hpp> 
#include <boost/archive/xml_oarchive.hpp> 
#include <boost/archive/binary_iarchive.hpp> 
#include <boost/archive/binary_oarchive.hpp> 
#include <iostream> 
#include <fstream> 
#include <sstream>

class Camera {

public:
    int id;
    std::string name;
    double pos;
};

namespace boost {
    namespace serialization {

        template<class Archive>
        void serialize(Archive& archive, Camera& cam, const unsigned int version)
        {
            archive & BOOST_SERIALIZATION_NVP(cam.id);
            archive & BOOST_SERIALIZATION_NVP(cam.name);
            archive & BOOST_SERIALIZATION_NVP(cam.pos);
        }

    } // namespace serialization
} // namespace boost

std::ostream& operator<<(std::ostream& cout, const Camera& cam)
{
    cout << cam.id << std::endl
        << cam.name << std::endl
        << cam.pos << std::endl;
    return cout;
}

void save()
{
    std::ofstream file("archive.xml");
    boost::archive::xml_oarchive oa(file);
    
    Camera cam;
    cam.id = 100;
    cam.name = "new camera";
    cam.pos = 99.88;

    oa & BOOST_SERIALIZATION_NVP(cam);
}

void load()
{
    std::ifstream file("archive.xml");
    boost::archive::xml_iarchive ia(file);
    Camera cam;
    ia & BOOST_SERIALIZATION_NVP(cam);
    std::cout << cam << std::endl;
}

void test_camera()
{
    save();
    load();
}

int main(int argc, char** argv)
{
    test_camera();
}

binary archive

void save_load_with_binary_archive()
{
    // binary archive with stringstream
    std::ostringstream oss;
    boost::archive::binary_oarchive oa(oss);

    Camera cam;
    cam.id = 100;
    cam.name = "new camera";
    cam.pos = 99.88;

    oa & (cam);

   # get binary content
    std::string str_data = oss.str();
    std::cout << str_data << std::endl;

    std::istringstream iss(str_data);
    boost::archive::binary_iarchive ia(iss);
    Camera new_cam;
    ia & (new_cam);
    std::cout << new_cam << std::endl;
}

binary archive with poco SocketStream

client.cpp

void test_client()
{
    SocketAddress address("127.0.0.1", 9911);
    StreamSocket socket(address);
    SocketStream stream(socket);
    //Poco::StreamCopier::copyStream(stream, std::cout);

    boost::archive::binary_oarchive oa(stream);
    Camera cam;
    cam.id = 100;
    cam.name = "new camera";
    cam.pos = 99.88;

    oa & (cam);
}

server.cpp

void run()
    {
        Application& app = Application::instance();
        app.logger().information("Request from " + this->socket().peerAddress().toString());
        try
        {
            SocketStream stream(this->socket());
            //Poco::StreamCopier::copyStream(stream, std::cout);

            boost::archive::binary_iarchive ia(stream);
            Camera new_cam;
            ia & (new_cam);
            std::cout << new_cam << std::endl;
        }
        catch (Poco::Exception& exc)
        {
            app.logger().log(exc);
        }
    }

notes on std::string

Even know you have seen that they do the same, or that .data() calls .c_str(), it is not correct to assume that this will be the case for other compilers. It is also possible that your compiler will change with a future release.

2 reasons to use std::string:

std::string can be used for both text and arbitrary binary data.

//Example 1
//Plain text:
std::string s1;
s1 = "abc";
s1.c_str();

//Example 2
//Arbitrary binary data:
std::string s2;
s2.append("a\0b\0b\0", 6);
s2.data();

boost archive style

intrusive

`private template<class Archive>
void serialize(Archive& archive, const unsigned int version)`
friend class boost::serialization::access;

class Camera {

public:
    int id;
    std::string name;
    double pos;

private:
    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive& archive, const unsigned int version)
    {
        archive & BOOST_SERIALIZATION_NVP(id);
        archive & BOOST_SERIALIZATION_NVP(name);
        archive & BOOST_SERIALIZATION_NVP(pos);
    }
};

non-intrusive

class Camera {

public:
    int id;
    std::string name;
    double pos;
};


namespace boost {
    namespace serialization {

        template<class Archive>
        void serialize(Archive& archive, Camera& cam, const unsigned int version)
        {
            archive & BOOST_SERIALIZATION_NVP(cam.id);
            archive & BOOST_SERIALIZATION_NVP(cam.name);
            archive & BOOST_SERIALIZATION_NVP(cam.pos);
        }

    } // namespace serialization
} // namespace boost

boost archive type

shared_ptr

boost::shared_ptr<T> instead of std::shared_prt<T>
and

#include <boost/serialization/shared_ptr.hpp>

Reference

History

20180128: created.
20180129: add intrusive,non-intrusive part.

Copyright

Post author: kezunlin
Post link: https://kezunlin.me/post/6887a6ee/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 3.0 unless stating additionally.

如何在C++中使用boost库序列化自定义class ？| serialize and deserialize a class