boost serialization, deserialization of raw C arrays

boost, boost-serialization, c++, serialization

Solution

I heartily recommend you use `std::array` or `std::vector` here, because... you messed this up :)

For starters, `Monkey` doesn't initialize its members. So, loading ends up doing a `load_binary` to whatever pointer value `m.arr` happened to have. How would you expect the deserialization to "know" that you needed to allocate memory for that? You need to tell it:

    template<class Archive>
    void serialize(Archive & ar, Monkey& m, const unsigned int version)
    {
        ar & m.num;
        if (Archive::is_loading::value)
        {
            assert(m.arr == nullptr);
            m.arr = new float[m.num];
        }
        ar & make_array<float>(m.arr, m.num);
    }

Now, let's make `Monkey` a bit less unsafe (by adding initialization and destruction, and, perhaps most importantly, prohibiting copy semantics):

struct Monkey
{
    uint32_t num;
    float* arr;

    Monkey() : num(0u), arr(nullptr) {}

    Monkey(Monkey const&) = delete;
    Monkey& operator=(Monkey const&) = delete;
    ~Monkey() { delete[] arr; }
};

Now, you can see it work:

#include <iostream>
#include <fstream>
#pragma warning(disable: 4244)
#include <boost/serialization/serialization.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>

struct Monkey
{
    uint32_t num;
    float* arr;

    Monkey() : num(0u), arr(nullptr) {}

    Monkey(Monkey const&) = delete;
    Monkey& operator=(Monkey const&) = delete;
    ~Monkey() { delete[] arr; }
};

namespace boost
{
    namespace serialization
    {
        template<class Archive>
        void serialize(Archive & ar, Monkey& m, const unsigned int version)
        {
            ar & m.num;
            if (Archive::is_loading::value)
            {
                assert(m.arr == nullptr);
                m.arr = new float[m.num];
            }
            ar & make_array<float>(m.arr, m.num);
        }
    }
}

int main(int argc, char* argv[])
{
    const char* name = "monkey.txt";
    {
        Monkey m;
        m.num = 10;
        m.arr = new float[m.num];
        for (uint32_t index = 0; index < m.num; index++)
            m.arr[index] = (float)index;

        std::ofstream outStream(name, std::ios::out | std::ios::binary | std::ios::trunc);
        boost::archive::binary_oarchive oar(outStream);
        oar << (m);
    }

    Monkey m;
    std::ifstream inStream(name, std::ios::in | std::ios::binary);
    boost::archive::binary_iarchive iar(inStream);
    iar >> (m);

    std::copy(m.arr, m.arr + m.num, std::ostream_iterator<float>(std::cout, ";"));
}

Prints

0;1;2;3;4;5;6;7;8;9;

Live on Coliru

Problem

I'm trying to serialize and deserialize raw C pointers and their data, with the example below. It seems to serialize just fine, but I am unsure how to make it deserialize - it just crashes with a memory access violation exception when I deserialize it. I suppose it is because it dosn't know how to deserialize it, but where do I specify that? Using a vector is not an option, in very large primitive data amounts it is painfully slow ``` #include <stdint.h> #include <string> #include <iostream> #include <fstream> #pragma warning (push) #pragma warning( disable : 4244 ) #include <boost/serialization/serialization.hpp> #include <boost/serialization/vector.hpp> #include <boost/serialization/string.hpp> #include <boost/serialization/array.hpp> #include <boost/archive/binary_oarchive.hpp> #include <boost/archive/binary_iarchive.hpp> #pragma warning (pop) struct Monkey { uint32_t num; float* arr; }; namespace boost { namespace serialization { template<class Archive> void serialize(Archive & ar, Monkey& m, const unsigned int version) { ar & m.num; ar & make_array<float>(m.arr, m.num); } } } int _tmain(int argc, _TCHAR* argv[]) { const char* name = "monkey.txt"; { Monkey m; m.num = 10; m.arr = new float[m.num]; for (uint32_t index = 0; index < m.num; index++) m.arr[index] = (float)index; std::ofstream outStream(name, std::ios::out | std::ios::binary | std::ios::trunc); boost::archive::binary_oarchive oar(outStream); oar << (m); } Monkey m; std::ifstream inStream(name, std::ios::in | std::ios::binary); boost::archive::binary_iarchive iar(inStream); iar >> (m); return 0; } ```

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