Understanding typedefs for function pointers in C

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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 to such a definition while trying to understand a numerical algorithm written in C a while ago. So, could you share your tips and thoughts on how to write good typedefs for pointers to functions (Do's and Do not's), as to why are they useful and how to understand others' work? Thanks!

function-pointers typedef c
7 Answers

Use typedef's 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

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