Re: [Boost-users] Fwd: Serializing of object with map and multimap. Questions.

Subject: Re: [Boost-users] Fwd: Serializing of object with map and multimap. Questions.
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2009-11-05 03:44:09

On Thu, Nov 5, 2009 at 1:33 AM, B Hart <bhartsb_at_[hidden]> wrote:
> I have sent a couple of questions to this list in the past week and haven't
> gotten a single response.  Wondering if my messages are being bounced???
>
> ---------- Forwarded message ----------
> From: B Hart <bhartsb_at_[hidden]>
> Date: Wed, Nov 4, 2009 at 3:42 PM
> Subject: Serializing of object with map and multimap. Questions.
> To: Boost-users_at_[hidden]
>
>
> I've been having some problems storing and loading a class with a map and a
> multimap.  The map contains values that are simple objects of another
> class.  My questions are below.  Here is also a link to the same question
> posted on stackoverflow.
> Thanks.
>
> http://stackoverflow.com/questions/1676781/boost-serializing-of-object-containing-map-with-object-values-and-multimap-wit
>
> See below a main() and two very simple classes. Then per Boost serialization
> (and what is shown) my questions are:
>
> 1) Does class B need the normal overloaded stream insertion operators '<<'
> and '>>' to be defined? Currently in my real code it doesn't have these.
>
> 2) Does class A in the store() and load() methods need to iterate through
> the map and multimap containers explicitly, storing/loading their key:value
> pairs explicitely? e.g. something like:
>
> void A::store(const char* filename){
>
>
>
> std::ofstream ofs(filename);
> boost::archive::text_oarchive oa(ofs);
>
>
>
> std::map< std::string, B >::iterator it;
>
>
> BMap.size();
> oa << BMap.size();
>
> for( it = BMap.begin(); it != BMap.end(); it++ ){
>
>
> Â  Â  Â  Â  oa << Â it->first;
> Â  Â  Â  Â  oa << it->second;
>
>
> }
>
> //similar for strMultimap
> }
>
> I assume that I don't need to do this, but am not certain.
>
> 3) Assuming class B has only the two data members shown, does it need a
> default contructor included explicitely? (as opposed to the implicit default
> constructor)
>
> 4) Does B need to have an overide for the comparison operator '>'? I assume
> that it doesn't since this is a very simple class.
>
> Finally, any other comments per anything that I've failed to cover is
> appreciated!
>
> Example code for my above questions:
>
> //includes ommitted
>
> int main() {
>
>
> Â  Â  std::string file("test.dat");
>
>
> Â  Â  A * pA = new A;
>
>
> Â  Â  pA->store(file.c_str());
>
> Â  Â  pA->fillMaps();
> Â  Â  //release data
> Â  Â  pA->load(file.c_str());
>
>
>
> Â  Â  return 0;
> }
>
> //includes ommitted
>
>
> class A
> {
> Â  Â  friend class boost::serialization::access;
>
>
>
> public:
>
> Â  Â  std::map< std::string, B > BMap;
>
>
> Â  Â  std::multimap< std::string, std::string > strMultimap;
>
>
>
> Â  Â  template<class Archive>
> Â  Â  void serialize(Archive & ar, const unsigned int version)
>
>
> Â  Â  {
> Â  Â  Â  Â  ar & BMap;
> Â  Â  Â  Â  ar & strMultimap;
>
> Â  Â  }
>
> Â  Â  void store(const char* filename){
>
>
> Â  Â  std::ofstream ofs(filename);
> Â  Â  boost::archive::text_oarchive oa(ofs);
>
>
> Â  Â  oa << this;
> Â  }
>
> Â  void load(const char* filename){
>
>
>
> Â  Â  std::ifstream ifs(filename);
> Â  Â  boost::archive::text_iarchive ia(ifs);
>
>
> Â  Â  ia >> this;
>
> Â  }
>
> Â  void fillMaps(){
>
>
> //code to allocate B objects and put them in BMap and fill strMultimap with
> whatever number of key:value pairs
>
> }
>
>
> class B
> {
> friend class boost::serialization::access;
>
>
>
> public:
>
> Â  Â  std::string str;
>
> Â  Â  unsigned int num;
>
> Â  Â  B::B(void)
>
> Â  Â  : str("a string")
> Â  Â  , num(7)
>
> Â  Â  {
> Â  Â  }
>
> Â  Â  template<class Archive>
>
> Â  Â  void serialize(Archive & ar, const unsigned int version)
>
>
> Â  Â  {
> Â  Â  Â  Â  ar & str;
> Â  Â  Â  Â  ar & num;
>
> Â  Â  }
> }

We see your emails.  I am not a Boost.Serialization guru though, but
let me see if I can help any (take anything I say with a grain of
salt, I use Boost.Serialization, but it seems to just 'work' for me
most of the time so I do not know much about it):

1)  I do not think so, just either an internal or external
Boost.Serialization streaming functions as normal.

2)  No, Boost.Serialization should already have overloads to handle
map's properly, if not then there is plenty of code (and I can post
mine that I map for the tr1 maps and set) out there to do that already
the 'proper' way.  :)

3)  You should not need to explicitly create a default constructor,
but the class must be default constructable (found that out the hard
way).

4)  Since you only use B as the data element of a map, no.

And the reason you might not be getting responses, you should title
your posts appropriately, at the front of you title you should put
[Serialization] as many people filter boost email based on the sub
library, so you title should have been.

[Serialization] Serializing of object with map and multimap. Questions.