使用內存映射文件進行序列化

Question

我想在內存映射文件上序列化我的類對象，但事實證明，boost序列化僅適用於文件流。 這是一個例子：

class gps_position
{
private:
    friend class boost::serialization::access;
    // When the class Archive corresponds to an output archive, the
    // & operator is defined similar to <<.  Likewise, when the class Archive
    // is a type of input archive the & operator is defined similar to >>.
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    {
        ar & degrees;
        ar & minutes;
        ar & seconds;
    }
    int degrees;
    int minutes;
    float seconds;
public:
    gps_position(){};
    gps_position(int d, int m, float s) :
        degrees(d), minutes(m), seconds(s)
    {}
};

int main() {
    // create and open a character archive for output
    std::ofstream ofs("filename");

    // create class instance
    const gps_position g(35, 59, 24.567f);

    // save data to archive
    {
        boost::archive::text_oarchive oa(ofs);
        // write class instance to archive
        oa << g;
        // archive and stream closed when destructors are called
    }

    // ... some time later restore the class instance to its orginal state
    gps_position newg;
    {
        // create and open an archive for input
        std::ifstream ifs("filename");
        boost::archive::text_iarchive ia(ifs);
        // read class state from archive
        ia >> newg;
        // archive and stream closed when destructors are called
    }
    return 0;
}

是否可以通過內存映射文件來完成。 我正在使用Windows API CreateFileMapping和MapViewOfFile進行內存映射。

編輯：

這是我嘗試使用boost iostream庫和內存映射文件執行的操作。

namespace io = boost::iostreams;
typedef io::stream_buffer < io::mapped_file_source > in_streambuf;
typedef io::stream_buffer < io::mapped_file_sink > out_streambuf;

int main() {
    // create and open a character archive for output
    //  std::ofstream ofs("filename");  /*commented this */

    boost::iostreams::mapped_file_params params;
        params.path  = "filepath";
    params.flags = io::mapped_file::mapmode::readwrite;

    out_streambuf obuf(params);
    std::ostream ofs(&obuf);

    // create class instance
    const gps_position g(35, 59, 24.567f);

    // save data to archive
    {
        boost::archive::text_oarchive oa(ofs);
        // write class instance to archive
        oa << g;
        // archive and stream closed when destructors are called
    }

    // ... some time later restore the class instance to its orginal state
    gps_position newg;
    {
        // create and open an archive for input
    in_streambuf ibuf(params);
    std::istream ifs(&ibuf);

        //std::ifstream ifs("filename");  /* commented this */

        boost::archive::text_iarchive ia(ifs);

        // read class state from archive

        ia >> newg;
        // archive and stream closed when destructors are called
    }
    return 0;
}

現在，我對boost不太熟悉，但是此代碼在運行時失敗。 因此，非常感謝您的幫助。 失敗本身發生在這里“ out_streambuf obuf（params）;”。 多謝你們！

Answer 1

您可能需要研究boost.interprocess bufferstream ：

bufferstream類為iostream接口提供了在固定大小的內存緩沖區中直接格式化的iostream接口，可防止緩沖區溢出。

Answer 2

五年后，

#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/mapped_region.hpp>
#include <boost/interprocess/streams/bufferstream.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
using namespace boost::interprocess;
....
_shm = new shared_memory_object(open_or_create,shm_name,read_write);
_shm->truncate(shm_size);
_reg = new mapped_region( _shm,read_write);
...
// write the serializable structure
obufferstream bs(static_cast<char*>(region.get_address()),_reg->get_size());
boost::archive::binary_oarchive arch(dynamic_cast<ostream&>(bs));
arch << my_struct;
...
// read the serializable structure
ibufferstream bs(static_cast<char*>(_reg->get_address()),_reg->get_size());
boost::archive::binary_oarchive arch(dynamic_cast<istream&>(bs));
arch >> my_struct;

等等！

Answer 3

存檔類僅適用於現有流，因此您需要一個能夠讀取/寫入映射的內存區域的流。 我不知道有任何現成的解決方案，因此您可能只需要編寫自己的streambuf類即可。 一旦有了這個，就很容易將它附加到標准istream ：

std::istream is(your_streambuf);
boost::archive::text_iarchive ia(is);
...