Simple C++ State machine implementation

SMImpl.cpp

// The transition table itself
SMTransition MyClass::transitionTable[] =  {
  { SMStateStart, SMEventAlpha, &MyClass::transToOne },
  { SMStateStart, SMEventBeta, &MyClass::transToTwo },
  ...
  { SMStateAny, SMEventAnyEvent, &MyClass::transDoNothing }
};

// Macro to give us the number of transitions in the table
#define TR_COUNT (sizeof(transitionTable) / sizeof(*transitionTable))

void MyClass::process() {
  if (nextEvent != SMNoEvent) {
    for (int i = 0; i < TRANSITION_COUNT; i++) {
      if (transitionTable[i].state == curState || transitionTable[i].state == SMAnyState) {
        if (transitionTable[i].event == nextEvent || transitionTable[i].event == SMAnyEvent) {
          curState = (this->*transitionTable[i].tFunc)();
          break;
        }
      }
    }
  }
}

// recEventB and on are basically the same, so just showing A here
void MyClass::recEventA() {
  // Validate or do some internal processing if we really need to but mainly just...
  nextEvent = SMEventAlpha; 
}

// Transition functions
SMState MyClass::transToStart() {
  // Do our work to get into the Start state. Initialize things, perhaps, or clear flags.
  nextEvent = SMEventNoEvent;
  return SMStateStart;
}

SMState MyClass::transToOne() {
  // Exactly as above: do whatever we need to do internally to be in the One state.
  nextEvent = SMEventNoEvent;
  return SMStateOne;
}

SMState MyClass::transDoNothing() {
  nextEvent = SMEventNoEvent;
  return curState;
}