namespace boost {
  namespace stacktrace {
    class stacktrace;

    // Outputs stacktrace in a human readable format to output stream. 
    template<typename CharT, typename TraitsT> 
      std::basic_ostream< CharT, TraitsT > & 
      operator<<(std::basic_ostream< CharT, TraitsT > & os, 
                 const stacktrace & bt);
  }
}