boost serialization std::unique_ptr support

问题:

Does the boost serialization library support serialization of std::unique_ptr? I tried to compile the code below, but if I include the boost::archive::text_oarchive oa(ofs); oa << g; line,

the compiler (btw gcc4.7 with -std=c++11 flag) throws an error

/usr/include/boost/serialization/access.hpp:118:9: error: ‘class std::unique_ptr’ has no member named ‘serialize’

#include <iostream>
#include <memory>
#include <fstream>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
class MyDegrees
{
public:
  void setDeg(int d){deg = d;}
  int getDeg()const {return deg;}
private:
  friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    { ar & deg; }
  int deg;
};
class gps_position
{
private:
    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    { ar & degrees; }
    std::unique_ptr<MyDegrees> degrees;
public:
    gps_position(): degrees(std::unique_ptr<MyDegrees>(new MyDegrees)){};
    void setDeg(int d){degrees->setDeg(d);}
    int getDeg() const {return degrees->getDeg();}
};
int main()
{
    std::ofstream ofs("filename");
    gps_position g;
    g.setDeg(45);
    std::cout<<g.getDeg()<<std::endl;
    {// compiler error, fine if commented out
        boost::archive::text_oarchive oa(ofs); oa << g;
    }
  return 0;
}

回答1:

No, there is no out of the box adaption. You will need to provide a non-intrusive adapter yourself. See the tutorial here to get an idea how to do that.

回答2:

I'm not sure how to interpret this list, but it seems like support for this was added sometime after 1.48. I am using 1.58 and it is included. Just

#include <boost/serialization/unique_ptr.hpp>

and then it will work as follows:

#include <memory>

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/unique_ptr.hpp>

#include <fstream>

class Point
{
public:
    Point() { }

    float x = 1.;
    float y = 2.;
    float z = 3.;

private:
    friend class boost::serialization::access;

    template<class TArchive>
    void serialize(TArchive & archive, const unsigned int version)
    {
        archive & x;
        archive & y;
        archive & z;
    }
};

void ValidUniquePointer()
{
    std::unique_ptr<Point> p(new Point());

    std::ofstream outputStream("test.txt");
    boost::archive::text_oarchive outputArchive(outputStream);
    outputArchive << p;
    outputStream.close();

    // read from a text archive
    std::unique_ptr<Point> pointRead;
    std::ifstream inputStream("test.txt");
    boost::archive::text_iarchive inputArchive(inputStream);
    inputArchive >> pointRead;

    std::cout << pointRead->x << " " << pointRead->y << " " << pointRead->z << std::endl;

}

void NullUniquePointer()
{
    std::unique_ptr<Point> p;

    std::ofstream outputStream("test.txt");
    boost::archive::text_oarchive outputArchive(outputStream);
    outputArchive << p;
    outputStream.close();

    // read from a text archive
    std::unique_ptr<Point> pointRead;
    std::ifstream inputStream("test.txt");
    boost::archive::text_iarchive inputArchive(inputStream);
    inputArchive >> pointRead;

    if(pointRead != nullptr) {
        std::cout << pointRead->x << " " << pointRead->y << " " << pointRead->z << std::endl;
    }
    else {
        std::cout << "Pointer is null!" << std::endl;
    }

}

int main()
{
    ValidUniquePointer();
    NullUniquePointer();
    return 0;
}

回答3:

as mentioned by pmr, I managed to come up the following solution, and at the first glance, everything works. In hope that someone could find it useful:

#include <iostream>
#include <memory>
#include <fstream>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
namespace boost { 
namespace serialization {

template<class Archive, class T>
inline void save(
    Archive & ar,
    const std::unique_ptr< T > &t,
    const unsigned int /*file_version*/
){
    // only the raw pointer has to be saved
    const T * const base_pointer = t.get();
    ar & BOOST_SERIALIZATION_NVP(base_pointer);
}
template<class Archive, class T>
inline void load(
    Archive & ar,
    std::unique_ptr< T > &t,
    const unsigned int /*file_version*/
){
    T *base_pointer;
    ar & BOOST_SERIALIZATION_NVP(base_pointer);
    t.reset(base_pointer);
}
template<class Archive, class T>
inline void serialize(
    Archive & ar,
    std::unique_ptr< T > &t,
    const unsigned int file_version
){
    boost::serialization::split_free(ar, t, file_version);
}
} // namespace serialization
} // namespace boost

class MyDegrees
{
public:
  void setDeg(int d){deg = d;}
  int getDeg()const {return deg;}
private:
  friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    { ar & deg; }
  int deg;
};
class gps_position
{
private:
    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int version)
    { ar & degrees;  }
    std::unique_ptr<MyDegrees> degrees;
public:
    gps_position(): degrees(std::unique_ptr<MyDegrees>(new MyDegrees)){};
    void setDeg(int d){degrees->setDeg(d);}
    int getDeg() const {return degrees->getDeg();}
};
int main()
{
    std::ofstream ofs("filename");
    gps_position g;
    g.setDeg(45);
    std::cout<<g.getDeg()<<std::endl;
    { boost::archive::text_oarchive oa(ofs); oa << g; }
    gps_position newg;
    {
        std::ifstream ifs("filename");
        boost::archive::text_iarchive ia(ifs);
        ia >> newg;
        std::cout<<newg.getDeg()<<std::endl;
    }
  return 0;
}

回答4:

recent versions of boost serialization provide support for all std smart pointer types.