How to serialize boost::dynamic_bitset?

Question

How to serialize a class with a boost::dynamic_bitset member?

#include 
#include 

        

Answer 1

dynamic_bitset<> is not serializable, as you've found out (std::bitset is different type).

Not to worry, though, you can add it without too much effort:

namespace boost { namespace serialization {

    template 
        void save(Ar& ar, dynamic_bitset const& bs, unsigned) {
            size_t num_bits = bs.size();
            std::vector blocks(bs.num_blocks());
            to_block_range(bs, blocks.begin());

            ar & num_bits & blocks;
        }

    template 
        void load(Ar& ar, dynamic_bitset& bs, unsigned) {
            size_t num_bits;
            std::vector blocks;
            ar & num_bits & blocks;

            bs.resize(num_bits);
            from_block_range(blocks.begin(), blocks.end(), bs);
            bs.resize(num_bits);
        }

    template 
        void serialize(Ar& ar, dynamic_bitset& bs, unsigned version) {
            split_free(ar, bs, version);
        }

} }

This works e.g. Live On Coliru

int main() {
    A a;
    for (int i=0; i<128; ++i)
        a.x.resize(11*i, i%2);

    std::stringstream ss;
    {
        boost::archive::text_oarchive oa(ss);
        oa << a;
    }
    std::cout << ss.str();
    {
        boost::archive::text_iarchive ia(ss);
        A b;
        ia >> b;

        assert(a.x == b.x);
    }
}

Note that if you can't afford to copy the blocks vector, it's equally easy to add serialization directly on the m_bits level, but that requires intrusive changes (friend access required at a minimum).

Such a thing would easily be added to boost in a pull request.

Update added that pull request