I'm trying to chain debugging logs together with a filtering_ostream. I've discovered that I need to call flush() on the filtering_ostream to get characters to appear in console in a timely fashion. This flush() call doesn't causes the file to be flushed. After some digging, I've discovered that the boost::iostreams::file_sink doesn't have the flushable_tag (or implement flush). std::fstream does have a flush function, and if I use it directly (not chained into a filtering_ostream), the flush call works as you might expect. So what is the appropriate way of implementing this? Chaining multiple logs together seems like a great way to use iostreams library. And out of curiosity, why doesn't file_sink implement flushable_tag? Here is the code I was using: #include <boost/iostreams/stream.hpp> #include <boost/iostreams/device/file.hpp> #include <boost/iostreams/stream.hpp> #include <boost/iostreams/tee.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/categories.hpp> #include <boost/iostreams/concepts.hpp> #include <boost/thread.hpp> #include <boost/thread/xtime.hpp> #include <iostream> int main(int argc, char** argv) { using namespace std; using namespace boost; using namespace boost::iostreams; filtering_ostream fo; file_sink fsink("out.txt"); tee_filter<file_sink> tee_fsink(fsink); fo.push(tee_fsink); fo.push(cout); int i = 0; while(true) { fo << i << " "; //without this, I don't see "one print / second" //with it, I only see them on cout, but not in out.txt. fo.flush(); i++; boost::xtime xt; boost::xtime_get(&xt, boost::TIME_UTC); xt.sec += 1; boost::thread::sleep(xt); } return 0; } tx Andy