How do I serialize a class containing pointers to primitives? - c++

Question

I am trying to use boost's functionality for serializing pointers to primitives (so that I don't have to de-reference and do a deep store myself). However, I get a pile of errors when I try to do it. Here is a simple example of a class that is supposed to contain save and load methods which write and read the class content from a file. This program does not compile:
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/shared_ptr.hpp>
#include <fstream>
class A
{
public:
boost::shared_ptr<int> sp;
int const * p;
int const& get() {return *p;}
void A::Save(char * const filename);
static A * const Load(char * const filename);
//////////////////////////////////
// Boost Serialization:
//
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive & ar,const unsigned int file_version)
{
ar & p & v;
}
};
// save the world to a file:
void A::Save(char * const filename)
{
// create and open a character archive for output
std::ofstream ofs(filename);
// save data to archive
{
boost::archive::text_oarchive oa(ofs);
// write the pointer to file
oa << this;
}
}
// load world from file
A * const A::Load(char * const filename)
{
A * a;
// create and open an archive for input
std::ifstream ifs(filename);
boost::archive::text_iarchive ia(ifs);
// read class pointer from archive
ia >> a;
return a;
}
int main()
{
}
Note that I am not interested in a solution that dereferences the pointer; I want boost to take care of that for me (many of these classes might be pointing to the same underlying object).

Answer 1

In http://www.boost.org/doc/libs/1_54_0/libs/serialization/doc/index.html:
By default, data types designated primitive by Implementation Level
class serialization trait are never tracked. If it is desired to track
a shared primitive object through a pointer (e.g. a long used as a
reference count), It should be wrapped in a class/struct so that it is
an identifiable type. The alternative of changing the implementation
level of a long would affect all longs serialized in the whole program
- probably not what one would intend.
Hence:
struct Wrapped {
int value;
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive & ar,const unsigned int file_version)
{
ar & value;
}
};
boost::shared_ptr<Wrapped> sp;
Wrapped const * p;