Understanding typedefs for function pointers in C

Question

I have always been a bit stumped when I read other peoples\' code which had typedefs for pointers to functions with arguments. I recall that it took me a while to get around

Answer 1

Use typedefs to define more complicated types i.e function pointers

I will take the example of defining a state-machine in C

    typedef  int (*action_handler_t)(void *ctx, void *data);

now we have defined a type called action_handler that takes two pointers and returns a int

define your state-machine

    typedef struct
    {
      state_t curr_state;   /* Enum for the Current state */
      event_t event;  /* Enum for the event */
      state_t next_state;   /* Enum for the next state */
      action_handler_t event_handler; /* Function-pointer to the action */

     }state_element;

The function pointer to the action looks like a simple type and typedef primarily serves this purpose.

All my event handlers now should adhere to the type defined by action_handler

    int handle_event_a(void *fsm_ctx, void *in_msg );

    int handle_event_b(void *fsm_ctx, void *in_msg );

References:

Expert C programming by Linden