Hmmm - I think the map size is already saved to disk. If you just copy the current templated implementation for map loading and instantiate a specialized version for your case, I would think that would handle the job. Robert Ramey ------------------------------------------------------- I am sorry. However, I do not quite understand. Let me more specific to my case. I have a data structure: map<const FiducialPair *, vector<RectPair> > fiducialPairSearchRegionMap; Both FiducialPair and RectPair can be serialized with boost no problem. I try to serialize the whole map by void save(Archive & ar, const unsigned int version) const { ar & fiducialPairSearchRegionMap; } void load(Archive & ar, const unsigned int version) { ar & fiducialPairSearchRegionMap; } I would get the following error: C:\Boost\include\boost-1_33_1\boost\archive\detail\iserializer.hpp(487): error C2440: 'reinterpret_cast' : cannot convert from 'typef *__w64 ' to 'void ** ' C:\Boost\include\boost-1_33_1\boost\archive\detail\iserializer.hpp(493): error C2664: 'T *boost::archive::detail::load_pointer_type<Archive,Tptr>::pointer_tweak<const FiducialPair>(const boost::serialization::extended_type_info &,void *,T &)' : cannot convert parameter 2 from 'typef ' to 'void *' with [ T=const FiducialPair, Archive=boost::archive::text_iarchive, Tptr=typef ] Conversion loses qualifiers May I know how I can apply ur suggested solution to my case? Thank you. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com