> - What is the variable atomic in the parameters of Data()=3F IIRC when atomic == true Data() is expected to contain a single and complete MIDI message. With atomic == false you could in theory send a MIDI message in segments perhaps (for a large sysex dump), but in practice I think the message callback will not be called for messages sent with atomic == false. > - And what is the Key Word "mutable" before BLocker=3F none of the book I > have about C++ talk about. If a member is declared mutable it can be changed by a member function declared const. I recommend "The C++ programming language" by Stroustrup. --martijn