Re: [Boost-users] serialization of vector of pointers

From: Stathis (stathis_at_[hidden])
Date: 2007-12-01 19:33:49

Robert Ramey wrote:
> Good call - two issues
> 
> a) using built-in serialization of collections
> b) saving a pointer to a primitive will result in untracked pointers.
> The proposed solution below addresses this second consideration.
> 
> Robert Ramey
> 
> Sohail Somani wrote:
>> On Sat, 01 Dec 2007 08:21:47 +0100, Stathis wrote:
>>
>>> Hi,
>>>
>>> What is the right way to serialize/deserialize a container of
>>> pointers, e.g. std::vector< int* > ? I want to store the values, not
>>> the addresses in this case. Should I just flatten my data and store
>>> it in a different fashion, then read the flat data and build my
>>> objects with a builder?
>> I think the main reason is that Boost Serialization doesn't track
>> pointers to the primitives. So I have a feeling you want to use
>> BOOST_STRONG_TYPEDEF (or whatever it is) and use a vector of those
>> things.
>>
>> Then #include <boost/serialization/vector.hpp> and ar & vec_of_ptrs
>>
>> If I am not mistaken, I think the magic should take over from there. 
> 
> 
> 
> _______________________________________________
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> Boost-users_at_[hidden]
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Hi again,

Thanks for the information. I did look at what you suggested, but it doesn't work when I reduce it 
to my case. If instead of a std::list<A*> somelist, I have std::list<int*> it doesn't handle the 
serialization of the list (it doesn't compile). Am I not supposed to use it like this?

Even when I use BOOST_STRONG_TYPEDEF to define a new type of int and try to serialize a list of that 
type, it still doesn't work.

Here is two things I have tried:

<snip>

#include <fstream>

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

#include <boost/serialization/list.hpp>

#define TESTFILE "test.txt"

int main( int /* argc */, char* /* argv */[] )
{
     std::list<int*> alist;
     alist.push_back(new int);
     {
         std::ofstream os( TESTFILE );
         boost::archive::text_oarchive oa(os);
         oa << alist;
     }

     std::list<int*> alist1;
     {
         std::ifstream is( TESTFILE );
         boost::archive::text_iarchive ia(is);
         ia >> alist1;
     }

     return 0;
}

</snip>

The one above doesn't compile.

I also wrote a different example case:

<snip>

#include <fstream>

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

#include <boost/serialization/list.hpp>

#define TESTFILE "test.txt"

class B
{
private:
     friend class boost::serialization::access;
     template<class Archive>
     void serialize(Archive & ar, const unsigned int version)
     {
         ar & myVar;
     }
     int myVar;
        
public:
     B(){};
        
};

class A
{

     friend class boost::serialization::access;
     template<class Archive>
     void serialize(Archive & ar, const unsigned int version)
     {
         ar & stuff;
     }
        
     std::list<B *> stuff;
        
public:
     A(){}
};

int main( int /* argc */, char* /* argv */[] )
{
     const A objA;
     {
         std::ofstream os( TESTFILE );
         boost::archive::text_oarchive oa(os);
         oa << objA;
     }

        A objB;
     {
         std::ifstream is( TESTFILE );
         boost::archive::text_iarchive ia(is);
         ia >> objB;
     }

     return 0;
}

</snip>

which works, but if I change:
  std::list<B *> stuff; // in class A
to
  std::list<int *> stuff;

it fails to compile.

Can you explain what is wrong with my intended use case and if possible how to do it properly?
Thank you for the help.

regards,
--stathis