difference between NULL and nil?

command-double-click is your friend

/* A null pointer constant. */
#if defined (STDDEFH) || defined (_needNULL)
#undef NULL /* in case <stdio.h> has defined it. */
#ifdef _GNUG_
#define NULL __null
#else /* G++ */
#ifndef __cplusplus
#define NULL ((void *)0)
#else /* C++ */
#define NULL 0
#endif /* C++ */
#endif /* G++ */
#endif /* NULL not defined and <stddef.h> or need NULL. */
#undef _needNULL

#ifndef NULL
#define NULL _DARWINNULL
#endif /* ! NULL */
#ifndef nil
 #define nil NULL
#endif /* ! nil */

Apparently holding down the command key and double clicking on a variable brings up a window with a list of files where that variable is defined. (Something I did not know. Guess I learn something new every day! 🙂 .)

I assume you know how #define works.

Therefore if you have:

#define nil NULL

It means that the compiler is actually replacing every occurrence of nil with NULL.

So they are exactly the same.

Message was edited by: Nitzan Wilnai

In theory, nil is used in the context of an object pointer, while NULL is for generic C pointers.