Direct boost serialization to char array

Boost serialization doc's assert that the way to serialize/deserialize items is using a binary/text archive with a stream on the underlying structure. This works fine if I wan't to use the serialized data as an std::string, but my i开发者_如何学Pythonntention is to convert it directly to a char* buffer. How can I achieve this without creating a temporary string?

Solved! For the ones that wanted a example:

char buffer[4096];

boost::iostreams::basic_array_sink<char> sr(buffer, buffer_size);  
boost::iostreams::stream< boost::iostreams::basic_array_sink<char> > source(sr);

boost::archive::binary_oarchive oa(source);

oa << serializable_object; 

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If you do not know the size of the data you are sending in advance, this is a generic way to serialize into an std::string:

// serialize obj into an std::string
std::string serial_str;
boost::iostreams::back_insert_device<std::string> inserter(serial_str);
boost::iostreams::stream<boost::iostreams::back_insert_device<std::string> > s(inserter);
boost::archive::binary_oarchive oa(s);

oa << obj;

// don't forget to flush the stream to finish writing into the buffer
s.flush();

// now you get to const char* with serial_str.data() or serial_str.c_str()

To deserialize, use

// wrap buffer inside a stream and deserialize serial_str into obj
boost::iostreams::basic_array_source<char> device(serial_str.data(), serial_str.size());
boost::iostreams::stream<boost::iostreams::basic_array_source<char> > s(device);
boost::archive::binary_iarchive ia(s);
ia >> obj;

This works like a charm, I use this to send data around with MPI.

This can be done very fast if you keep the serial_str in memory, and just call serial_str.clear() before you serialize into it. This clears the data but does not free any memory, so no allocation will happen when your next serialization data size does not require it.

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IIUC, you would like to write to a preallocated array of fixed size.

You could use a boost::iostreams::array_sink (wrapped with stream to give it an std::ostream interface) for that.

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Simpler version than accepted answer using std::stringstream :

// access data with .data() and size with .size()
using RawDataBuffer = std::string;

RawDataBuffer serialize(const Foo &obj) {
    std::stringstream ss;
    boost::archive::binary_oarchive oa(ss);

    oa << obj;

    return ss.str();
}

Foo deserialize(const RawDataBuffer &data) {
    std::stringstream ss(data);
    boost::archive::binary_iarchive ia(ss);

    Foo obj; // Foo must be default-constructible
    ia >> obj;

    return obj;
}

---

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Full working example compiled with boost 1.66 :

#include <boost/archive/binary_iarchive.hpp>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/serialization/access.hpp>
#include <sstream>
#include <iostream>


class Foo {
public:
    Foo() = default;
    Foo(int i) : _i(i)
    {}

    int get() const
    { return _i; }

protected:
    friend class boost::serialization::access;

    template<class Archive>
    void serialize(Archive &ar, const unsigned int /* version */ )
    {
        ar & _i;
    }

private:
    int _i;
};


// access data with .data() and size with .size()
using RawDataBuffer = std::string;

RawDataBuffer serialize(const Foo &obj) {
    std::stringstream ss;
    boost::archive::binary_oarchive oa(ss);

    oa << obj;

    return ss.str();
}

Foo deserialize(const RawDataBuffer &data) {
    std::stringstream ss(data);
    boost::archive::binary_iarchive ia(ss);

    Foo obj; // Foo must be default-constructible
    ia >> obj;

    return obj;
}


int main()
{
    RawDataBuffer buff;

    {
        Foo fortyTwo(42);

        buff = serialize(fortyTwo);
    }
    {
        Foo reborn;

        reborn = deserialize(buff);

        std::cout << "Reborn from " << reborn.get() << std::endl;
    }
}