[boost] [serialization] problem deserializing vectors

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-09-29 01:40:04

The serialization library likes if serialized classes have default 
constructor. Seems like it's possible to avoid declaring default ctor with 
separate "load"/"save" functions, but this is not really necessary: I can put 
default ctor in private section, and everything works ok. 

The problem arises when deserializing vector of classes which private default 
ctor. Even though class has "friend class boost::serialization::access", I 
get compile errors.

The code is:
#include <boost/serialization/access.hpp>
#include <boost/serialization/vector.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>

#include <sstream>
#include <vector>
using namespace std;

class V {
public:
    V(int i) : m_i(i) {}
    
private:
    int m_i;    
    
private: // serialization support
    friend class boost::serialization::access;
    
    V() {}
    template<class Archive>
    void serialize(Archive& ar, unsigned version)
    {
        ar & m_i;
    }    
};

int main()
{
    stringstream ss;
    boost::archive::text_oarchive oa(ss);
    vector<V> v;
    oa << v;
    boost::archive::text_iarchive ia(ss);
    ia >> v;
    return 0;
}

And the errors are:
vload.cpp: In member function `void
   boost::serialization::stl::archive_input_seq<Archive,
   Container>::operator()(Archive&, Container&) [with Archive =
   boost::archive::basic_text_iarchive<std::istream>, Container =
   std::vector<V, std::allocator<V> >]':
/home/ghost/Work/boost/boost/serialization/collections_load_imp.hpp:98:   
instantiated from `void boost::serialization::stl::load_collection(Archive&, 
Container&) [with Archive = 
boost::archive::basic_text_iarchive<std::istream>, Container = std::vector<V, 
std::allocator<V> >, InputFunction = 
boost::serialization::stl::archive_input_seq<boost::archive::basic_text_iarchive<std::istream>, 
std::vector<V, std::allocator<V> > >, R = 
boost::serialization::stl::reserve_imp<std::vector<V, std::allocator<V> > >]'
/home/ghost/Work/boost/boost/serialization/vector.hpp:40:   instantiated from 
`void boost::serialization::load(Archive&, std::vector<U, Allocator>&, 
unsigned int) [with Archive = 
boost::archive::basic_text_iarchive<std::istream>, U = V, Allocator = 
std::allocator<V>]'
/home/ghost/Work/boost/boost/serialization/split_free.hpp:45:   instantiated 
from `static void boost::serialization::detail::loader<Archive, 
T>::invoke(Archive&, T&, unsigned int) [with Archive = 
boost::archive::basic_text_iarchive<std::istream>, T = std::vector<V, 
std::allocator<V> >]'
/home/ghost/Work/boost/boost/serialization/split_free.hpp:56:   instantiated 
from `void boost::serialization::split_free(Archive&, T&, unsigned int) [with 
Archive = boost::archive::basic_text_iarchive<std::istream>, T = 
std::vector<V, std::allocator<V> >]'
/home/ghost/Work/boost/boost/serialization/vector.hpp:57:   instantiated from 
`void boost::serialization::serialize(Archive&, std::vector<U, Allocator>&, 
unsigned int, int) [with Archive = 
boost::archive::basic_text_iarchive<std::istream>, U = V, Allocator = 
std::allocator<V>]'
/home/ghost/Work/boost/boost/serialization/iserializer.hpp:63:   instantiated 
from `void boost::serialization::iserializer<Archive, 
T>::load_object_data(boost::archive::basic_iarchive&, void*, unsigned int) 
const [with Archive = boost::archive::basic_text_iarchive<std::istream>, T = 
std::vector<V, std::allocator<V> >]'
/home/ghost/Work/boost/boost/archive/basic_text_oarchive.hpp:160:   
instantiated from here
vload.cpp:21: error: `V::V()' is private
/home/ghost/Work/boost/boost/serialization/collections_load_imp.hpp:36: error: 
within
   this context

I've worked around this problem by using access::create in 
collections_load_imp.hpp (after making the 'create' method public). But would 
be great if this is solved more elegangly.

- Volodya