But i need the correct positions for a buffer handling.

Please try updating your Boost version, this works for me with the last (1.54) release, adding: std::cout << "what[0] = " << std::string(what[0].first, what[0].second) << std::endl; std::cout << "location = " << what.prefix().second - what.prefix().first << " length = " << what[0].second - what[0].first << std::endl; Produces: what[0] =