I've created a device with the boost::iostreams::dual_seekable category to use with the boost::iostreams::stream class, but I'm having trouble implementing seek. When I call seekp on the stream, seek on my device is called with a which (openmode) of both BOOST_IOS::in and BOOST_IOS::out. I would have expected for a call to seekp the which parameter in the seek call on my device would be BOOST_IOS::out, and calling seekg would set which to BOOST_IOS::in. The following code in boost\iostream\detail\streambuf\indirect_streambuf.hpp ignores the which argument passed and passes on through both in and out. template<typename T, typename Tr, typename Alloc, typename Mode> inline typename indirect_streambuf<T, Tr, Alloc, Mode>::pos_type indirect_streambuf<T, Tr, Alloc, Mode>::seekpos (pos_type sp, BOOST_IOS::openmode) { return seek_impl( position_to_offset(sp), BOOST_IOS::beg, BOOST_IOS::in | BOOST_IOS::out ); } Is this correct, and if so how do I implement seeking when using a dual head device? Many thanks, Steve Nutt