Is there any way to apply a filter temporarily ? I want to do this... io::filtering_ostream out; out.push_back(file_sink("my_file.txt")); out << "Authentication: "; out.push_front ( base64_encoder() ); // pseudo-code... see *push_front* instead of *push* out << make_ntlm_auth_from_system(); // this have to be base64 encoded out.pop_front(); // removes the base64_encoder out << "......"; // *NO* base64 encoded I don't want to do this... io::filtering_ostream out; out.push(file_sink("my_file.txt")); out << "Authentication: "; out.pop(); out.push(base64_encoder()); out.push(file_sink("my_file.txt")); out << make_ntlm_auth_from_system(); out.pop(); out.pop(); out.push(file_sink("my_file.txt")); out << "......"; The function make_ntlm_auth_from_system() creates an object that is *OStreamable*. Any other suggestions are welcome. :) Thanks and regards, Fernando.