I was looking through the iostreams sources and came across this in boost/iostreams/concepts.hpp: //------Definitions of helper templates for multi-character filter cncepts----// template struct multichar_filter : filter { struct category : filter::category, multichar_tag { }; }; template struct multichar_wfilter : multichar_filter { }; typedef multichar_filter<input> multichar_input_filter; typedef multichar_filter<input> multichar_input_wfilter; typedef multichar_filter<output> multichar_output_filter; typedef multichar_filter<output> multichar_output_wfilter; typedef multichar_filter multichar_dual_use_filter; typedef multichar_filter multichar_dual_use_wfilter; //-------------------------------------------------------------------------- --// It seems to me that the wide versions of these typedefs should be defined using multichar_wfilter, making the typedefs appear as follows: typedef multichar_filter<input> multichar_input_filter; typedef multichar_wfilter<input> multichar_input_wfilter; typedef multichar_filter<output> multichar_output_filter; typedef multichar_wfilter<output> multichar_output_wfilter; typedef multichar_filter multichar_dual_use_filter; typedef multichar_wfilter multichar_dual_use_wfilter; Also, the default arguments in multichar_filter and multichar_wfilter termplates aren't wrapped in BOOST_IOSTREAMS_DEFAULT_ARG(), unlike the other ones in this file. Seems like they should be, for consistency if nothing else. Chad