wchar_t based streams support GCC 2.95 and earlier does not provide this per default. Hence, the headers does not implement support for wchar_t streams for those compilers. Per default, wide character support is not assumed. If that is available for your environment, please define the preprocessor symbol FILEMM_WCHAR_SUPPORT before including filemm/streambuf.hh #define FILEMM_WCHAR_SUPPORT #ifndef FILEMM_streambuf # include <filemm/streambuf.hh> #endif Optionally, you can use the Autoconf macros provided in the file filemm.m4 shipped with this package. Put in your configure.ac file lines like AM_FILEMM_PATH AM_FILEMM_NEED_WCHAR_TRAITS([AM_FILEMM_HAVE_WCHAR_FUNCS]) AM_FILEMM_HAVE_WCHAR_SUPPORT and include the (optional) configuration header before including filemm/streambuf.hh #ifndef HAVE_CONFIG_H # include "config.h" // Name may vary depending on AC_CONFIG_HEADERS #endif #ifndef FILEMM_streambuf # include <filemm/streambuf.hh> #endif See also: Using FILE-- in your project