The boost serialization of float doesn't appear to use enough digits to guarantee that deserialization of a serialized value will produce the same value. The relevant code is in boost/archive/basic_text_oprimitive.hpp: void save(const float t) { os << std::setprecision(std::numeric_limits<float>::digits10 + 2); ... } std::numeric_limits<float>::digits10+2=8, but float actually requires numeric_limits<float>::max_digits10=9 decimal digits to guarantee unique representation. The code below (with boost/1.52) demonstrates the problem: #include <sstream> #include "boost/archive/text_iarchive.hpp" #include "boost/archive/text_oarchive.hpp" #include <iostream> int main(int argc, char **argv){ float oldf = -1.20786635e-05; std::ostringstream os; boost::archive::text_oarchive oa(os); oa & BOOST_SERIALIZATION_NVP(oldf); float newf; std::istringstream is(os.str()); boost::archive::text_iarchive ia(is); ia & BOOST_SERIALIZATION_NVP(newf); printf("before serialization: %.12g\nafter serialization: %.12g\n", oldf, newf); } // Output: // before serialization: -1.20786635307e-05 // after serialization: -1.20786644402e-05 Note: There's some discussion of this topic in a slightly different context here: http://boost.2283326.n4.nabble.com/serialization-Serialisation-deserialisati...