c program

"I wouldn't recommend nesting switch statements"

So how can you implement a State Machine without nesting switch statements?!

In each state, you need to consider each possible event - so that's inherently a "switch-within-a-switch", isn't it?

"I wouldn't recommend nesting switch statements"

So how can you implement a State Machine without nesting switch statements?!

In each state, you need to consider each possible event - so that's inherently a "switch-within-a-switch", isn't it?

I think Christoph means to avoid directly nesting switch statements, particularly with a lot of inline code in the cases:

   switch (a)
      {
      case a1 :
         switch (b)
            {
            case b1 :
               statement b1;
               switch (c)
                  {
                  ...
                  }
                break;
...

If each case just calls a function, those functions might happen to have switch statement inside, but won't cause readability and indentation problems. In fact, if every case in the switch calls a function, it's quite likely that it will compile into a jump table to those function calls, which is essentially the same code as a table of function pointers.

My faviourite (not!) is state machines where the states has not been given names. Each case just has a number, and within it the code may have a line:

state = 17;

Almost impossible to know what state 17 means, and almost impossible to insert a new state without missing to renumber all state changes.

My faviourite (not!) is state machines where the states has not been given names.

Ohhh, I think you forgot that for complete "enjoyment", all of the states are actually "documented" in a separate document, which is "slightly" out of date with the actual code. :)

(It's somewhere in the Writing-Unmaintainable-Code Howto: "Lie in the comments/documentation. It doesn't need to be obvious, just fail to keep the comments/documentation up to date with the code.")

If each case just calls a function, those functions might happen to have switch statement inside, but won't cause readability and indentation problems.

Exactly, thanks for guessing my thoughts.

#define STATE_INIT 0
#define STATE_WORK 1

void state_machine()
{
   static int current_state = STATE_INIT;

   switch(current_state)
   {
      case STATE_INIT:
         current_state = state_init();
         break;
      case STATE_WORK:
         current_state = state_work();
         break;
      default:
         current_state = STATE_INIT;
         break;
   }
}

int state_init()
{
   return(STATE_WORK);
}

int state_work()
{
   return(STATE_WORK);
}

Something along those lines.