State machines in C

Question

What is the best way to write a state machine in C?
I usually write a big switch-case statement in a for(;;), with callbacks to re-enter the state machine when an external

Answer 1

I use function pointers and a 2d look-up table where I use the state for one parameter and the event as the other.

I use excel (or any spreadsheet tool) to map a function to every state/event combination.

When an event occurs, I que it up, so then I have something that looks like this

int main(void)
{
    StateList currentState = start_up;
    EventList currentEvent;

    uint8_t stateArray[STATE_COUNT][EVENT_COUNT];

    InitializeStateArray(stateArray);
    InitializeEventQue();

    while(1)
    {
        currentEvent = GetPriorityEvent();
        currentState = (StateList)(*(stateArray[currentState][currentEvent]))();
    }
    return 1;  //should never get here
}

This method essentially forces the developer to consider all possible events in each state, and in my experience makes debugging a little easier.