CommandData uses the CommandDefinitions class to manage multiple devices... At least that's my intention. I have been battling for days with first the compiler and now the debugging engine. 

In my current compile, the single error message is "undefined reference to CommandDefinitions nextCommand();

in CommandDefinitions.h:
      bool nextCommand();

in CommandDefinitions.cpp:
bool CommandDefinitions::nextCommand() {
     if(commandReceived) {
           Serial.print("R");
     }
...
}

What I am seeing is that many methods in CommandDefinitions that appear to be properly declared and defined, but they get the "undefined" message.

And when I comment out those methods that won't compile, the remaining ones don't echo output from debug breakpoints... or even stop at a breakpoint.

The compile output is in the attached Zip as "output.txt".

And what version of C++ are we using here? That may be relevant.