Question

This question asks about a finite state machine with 100 states and each state having 100 events, and then does a brief comparison of using an if-else, switch statement, or function pointers to implement the state machine.

My question is: if using function pointers, how would the function pointers be appropriately set? With an if-else or a switch statement (in which case, would function pointers be more of a hybrid solution)? Or is there another way this is commonly done?

Answer 1

You could do something like below:

typedef int (*current_state) (void);
typedef int (*nextnew_state) (void);
struct FuncPointerState
{
  current_state curr_state;
  nextnew_state next_state;
}; 


/*init_state is the initial function state*/
struct FuncPointerState FpState = {init_state, NULL};     
int iRet = 0;

while(1)
{

   iRet = FpState.curr_state();
   if(iRet<= 0 )
   {
      return iRet;
   }
   if(NULL==FpState.next_state)
   {
     /* State Machine finished it's job */
      break;
   }
   FpState.curr_state = FpState.next_state;

}

Each state function should populate the next_state pointer. Also, you can modify the function pointers to take input arguments.