如何序列化boost库中的指针映射？

Question

我想序列化一个指针映射。

地图创建：

float *data = new float[1000];
std::map<int, std::map<std::string, float*> > mapa;
mapa[4]["foo"] = data;

将映射序列化到文件：

std::ofstream ofs("somefile");
boost::archive::binary_oarchive oa(ofs);
oa<<mapa;
ofs.close();

从文件加载地图：

std::ifstream ifs("somefile", std::ios::binary);
boost::archive::binary_iarchive ia(ifs);
std::map<int, std::map<std::string, float*> > newMapa;
ia >> newMapa;
ifs.close();

我怎样才能正确地做到这一点？

编译错误示例： https://godbolt.org/z/76fMbxMhf

Answer 1

强 typedef 旨在将原语包装成可跟踪的​​类型：https://www.boost.org/doc/libs/1_78_0/libs/serialization/doc/strong_typedef.html

BOOST_STRONG_TYPEDEF(float, Float)

但是，这将引入相当大的 (!) 开销，因为每个元素都需要跟踪。在您的示例中，将指针替换为数组索引会使 1000 倍更有意义。

当您使用它时，将其替换为 std::vector<float>，这样您就不会遇到终身问题（和泄漏）。

最后，在关闭文件甚至再次读取文件之前，请确保存档已完成。

参加 #1

Live On Coliru

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

#include <fstream>
#include <iostream>
#include <numeric>
#include <sstream>

using ConvolutedIndex = std::map<int, std::map<std::string, size_t>>;

int main()
{   
    auto data = std::vector<float>(1000);
    std::iota(data.begin(), data.end(), 0.0); // fill with sample data

    float* element = &data[rand() % data.size()]; // pick random element

    std::cout << "Random pick: " << *element << " at " << element << "\n";

    {
        std::ofstream                   ofs("filename", std::ios::binary);
        boost::archive::binary_oarchive oa(ofs);
        oa << ConvolutedIndex{
            {4,
             {
                 {"foo", element - data.data()},
             }},
        };
    } // also closes file, but more importantly, completes archive first

    {
        std::ifstream                   ifs("filename", std::ios::binary);
        boost::archive::binary_iarchive ia(ifs);

        ConvolutedIndex newMapa;
        ia >> newMapa;

        std::cout<< "The element recovered: " << data.at(newMapa.at(4).at("foo")) << "\n";
    }
}

打印例如

Random pick: 383 at 0x1f142dc
The element recovered: 383

参加 #2

这仍然有问题，因为您从未序列化被索引的浮点数。容易补救：

Live On Coliru

#include <boost/archive/binary_iarchive.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/serialization/map.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/string.hpp>
#include <boost/serialization/vector.hpp>

#include <fstream>
#include <iostream>
#include <numeric>
#include <sstream>

using Data            = std::vector<float>;
using ConvolutedIndex = std::map<int, std::map<std::string, size_t>>;

int main()
{   
    {
        Data data(1000);
        std::iota(data.begin(), data.end(), 0.0); // fill with sample data

        float* element = &data[rand() % data.size()]; // pick random element
        std::cout << "Random pick: " << *element << " at " << element << "\n";

        std::ofstream                   ofs("filename", std::ios::binary);
        boost::archive::binary_oarchive oa(ofs);

        oa << data << ConvolutedIndex{
            {4,
             {
                 {"foo", element - data.data()},
             }},
        };
    } // also closes file, but more importantly, completes archive first

    {
        std::ifstream                   ifs("filename", std::ios::binary);
        boost::archive::binary_iarchive ia(ifs);

        Data            newData;
        ConvolutedIndex newMapa;
        ia >> newData >> newMapa;

        std::cout<< "The element recovered: " << newMapa.at(4).at("foo") << "\n";
    }
}

现在每个人都很高兴（好吧，除了Gods of <random>，但读者需要做一些练习）：

Random pick: 383 at 0x1bd930c
The element recovered: 383