Implementing callback functions in C

Question

I am a newbie to C. I am trying to implement callback function using function pointers.

I am getting an error

:test_callback.c:10: error: expected identifier or ‘(’ before ‘void’

when I try to compile the following program:

#include<stdio.h>

void (*callback) (void);

void callback_proc ()
{
  printf ("Inside callback function\n");
}

void register ((void (*callback) (void)))
{
  printf ("Inside registration \n");
  callback (); /* Calling an initial callback with function pointer */
}

int main ()
{
  callback = callback_proc;/* Assigning function to the function pointer */
  register (callback);/* Passing the function pointer */
  return 0;
}

---

What is this error?Can anyone help?

Answer 1

1. register is a C keyword: Use another name for the function.

2. You have extra parantheses around the callback parameter. It should be:

   void funcName(void (*callback) (void))
   

Answer 2

I would recommend to use a typedef

#include<stdio.h>

typedef void (*callback_t) (void);
callback_t callback;

void callback_proc(void)
{
    printf ("Inside callback function\n");
}

void reg( callback_t _callback )
{
    printf ("Inside registration \n");
    _callback();
}

int main ()
{
    callback = callback_proc;
    reg(callback);

    return 0;
}

EDIT: removed the register issue