boost::serialization to serialize only the keys of a map

Question

I have a class with a map, and I want to serialize the class using boost serialize.

std::map<int, ComplicatedThing> stuff;

ComplicatedThing is derivable just by knowing the int. I want to serialize this efficiently. One way (ick, but works) is to make a vector of the keys and serialize the vector.

// illustrative, not test-compiled
std::vector<int> v;
std::copy(stuff.begin, stuff.end, std::back_inserter(v));
// or
for(std::vector<int> it = v.begin(); it != v.end(); it++)
    stuff[*it] = ComplicatedThing(*it);

// ...and later, at serialize/deserialize time
template<class Archive>
void srd::leaf::serialize(Archive &ar, const unsigned int version)
{
    ar & v;
}

But this is inelegant. Using BOOST_SERIALIZATION_SPLIT_MEMBER() and load/save methods, I think I should be able to skip the allocation of the intermediate vector completely. And there I am stuck.

Perhaps my answer lies in understanding boost/serialization/collections_load_imp.hpp. Hopefully there is a simpler path.

Andriy Tylychko · Accepted Answer · 2011-07-15T20:06:25.557

0

you can serialize it as list of ints (I don't mean std::list) instead of serializing it as a container (map or vector). fist write number of elements and then them one by one, deserizalize accordingly. it's 10 mins task. if you need this solution in many places, wrap map in your class and define serialization for it

edited Jul 15 '11 at 20:06

answered Jul 07 '11 at 14:10

Andriy Tylychko

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Thanks. Serializing is straight-forward that way, of course: for(it = v.begin(); it != v.end(); it++) ar & *it; but on deserialzing the loop isn't clear. Or do you mean ar & v.size(); for(it = v.begin(); it != v.end(); it++) ar & *it; so that I can build a loop on load? – jma Jul 07 '11 at 14:25
fist write number of elements and them them one by one, deserizalize accordingly – Andriy Tylychko Jul 07 '11 at 14:30

score 0 · Answer 2 · answered Jul 07 '11 at 14:49

If you want to make it not look clumsy, use range adaptors

 ar & (stuff | transformed(boost::bind(&map_type::value_type::first, _1));

Or if you include the appropriate headers, I suppose you could reduce this to

 ar & (stuff | transformed(&map_type::value_type::first))

Disclaimer

All of this assumes that Boost Serialization ships with serializers for Boost Ranges (haven't checked)
This might not work well in a bidirectional serialize setting (you'll want to read http://www.boost.org/doc/libs/1_46_1/libs/serialization/doc/serialization.html#splitting)
I haven't brought the above into the vicinity of a compiler

boost::serialization to serialize only the keys of a map

2 Answers2