hello, to get started with iostreams, i'm trying to write a multichar output filter that adds a string to the beginning and the end of whatever comes through. my code builds with a warning about unused parameter n and works - but only the first time, the second time, i get no output. i thought at first sending '\0' would trigger the stream's fail-bit or so, but out.good() returns true. any chance someone takes a look at my code and hazards a guess where the problem might be ? disclaimer: i was actually born and bred in C++ country long time ago, but i've been coding in python for a couple of years and got back only recently, so there's a good chance what i'm doing wrong is something really simple. guess you can tell from the code, it's been a while. good to be back though... :-) #include <iostream> #include <sstream> #include <boost/iostreams/concepts.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/operations.hpp> using std::cin; using std::cout; using std::endl; using std::streamsize; using std::string; using std::stringstream; class add_string_output_filter : public boost::iostreams::multichar_output_filter { public: template<typename Sink> streamsize write(Sink& sink, const char* s, streamsize n) { // remove trailing '\0' to prevent line break // TODO: there's probably a better way string tmp_string = string(s); string out_string = tmp_string.substr(0, tmp_string.size()-1); string pre_string("prepended string - "); string app_string(" - appended string"); stringstream sstrm; sstrm << pre_string << out_string << app_string << endl; // TODO: char* to string, back to char* ?!? return boost::iostreams::write(sink, sstrm.str().c_str(), sstrm.str().length()); } }; int main() { boost::iostreams::filtering_ostream out; out.push(add_string_output_filter()); out.push(cout); cout << "prompt: "; string str; while (getline(cin, str)) { out << str << endl; cout << "prompt: "; } } # sample session: prompt: some string prepended string - some string - appended string prompt: another string prompt: why no output ? prompt: # ssc