How do I read this complex declaration in C?

c

Solution

Start with the leftmost identifier and work your way out, remembering that `[]` and `()` bind before `*`, so `*a[]` is an array of pointers, `(*a)[]` is a pointer to an array, `*f()` is a function returning a pointer, and `(*f)()` is a pointer to a function:

       signal                                     -- signal
       signal(                          )         -- is a function
       signal(    sig,                  )         -- with a parameter named sig
       signal(int sig,                  )         --   of type int
       signal(int sig,        func      )         -- and a parameter named func
       signal(int sig,      (*func)     )         --   which is a pointer
       signal(int sig,      (*func)(   ))         --   to a function
       signal(int sig,      (*func)(int))         --     taking an int parameter
       signal(int sig, void (*func)(int))         --     and returning void
      *signal(int sig, void (*func)(int))         -- returning a pointer
     (*signal(int sig, void (*func)(int)))(   )   -- to a function
     (*signal(int sig, void (*func)(int)))(int)   --   taking an int parameter
void (*signal(int sig, void (*func)(int)))(int);  --   and returning void

`signal` associates a signal handler function `func` with a signal `sig`, and returns the pointer to the old signal handler function:

void new_interrupt_handler(int sig)
{
  ... // do something interesting with interrupt signal
}

int main(void)
{
  void (*old_interrupt_handler)(int);
  ...
  /**
   * Set up our new interrupt handler
   */
  old_interrupt_handler = signal(SIGINT, new_interrupt_handler);
  ...
  /**
   * Restore original interrupt handler
   */
  signal(SIGINT, old_interrupt_handler);
  ...
}

Problem

Original source

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