Hi all, I desire to use boost::iostream input and output filters. I cannot make the "Filter Usage Examples" (para2.2.2) shown here () to work. the following, as far as I can tell, is exactly the same "Ordinary OutputFilter" example shown at (http://tinyurl.com/45bur3o) struct toupper_filter { typedef char char_type; typedef boost::iostreams::output_filter_tag category; template<typename Sink> bool put(Sink& snk, char c) { return boost::iostreams::put(snk, toupper((unsigned char) c)); } }; the following code is modeled on the code at para2.2.2, "Filter Usage Examples": int main(int argc, char *argv[]) { // read my_input.txt and save uppercase version of text into datastore.txt std::ifstream pt_input; pt_input.open("my_input.txt"); std::ostringstream oss; oss << pt_input.rdbuf(); // oss now contains the text stored in input text boost::iostreams::filtering_ostream out_stream; // the following line is expected to transform the input text to uppercase. // instead it causes no text to appear in the output file. If the following line of // code is commented-out then contents of "my_input.txt" is placed in "datastore.txt". out_stream.push(toupper_filter()); out_stream.push(boost::iostreams::file_sink("datastore.txt")); out_stream.write( oss.str().c_str(), oss.str().length()); out_stream.flush(); } I am obviously doing not adding the toupper_filter into the filter chain correctly. Can anyone point out what I am doing wrong? many thanks