Appears as an issue in mapped_file.hpp if used with std::ios::in. Issue appears as a copy paste problem from mapped_file_source class. Issue manifest that const_begin() always return 0 (zero) and const_end() return 0+size(). To correct the problem const_data() method shall be called instead of data(). Below is diff with current version: --- \boost\include\boost-1_33_1\boost\iostreams\device\mapped_file.hpp.org +++ \boost\include\boost-1_33_1\boost\iostreams\device\mapped_file.hpp @@ -191,9 +191,9 @@ } const char* const_data() const { return delegate_.data(); } iterator begin() const { return data(); } - const_iterator const_begin() const { return data(); } + const_iterator const_begin() const { return const_data(); } iterator end() const { return data() + size(); } - const_iterator const_end() const { return data() + size(); } + const_iterator const_end() const { return const_data() + size(); } Please enter into bug database (do i need to subscribe to Track to do it myself?). Thanks, Igor