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Comment by loeg | Hacker News Reader

> b) NULL is not a useful macro. For example, > printf ("%p", NULL); > can have unexpected results.

How do you figure?

According to the fine standard, an implementation may #define NULL as either

  #define NULL ((void *) 0)

or just plain

  #define NULL 0

The latter works correctly because a literal 0 in pointer context is interpreted by the compiler as a null pointer.

If it is 0, the printf() provides no pointer context, so the 0 is interpreted as an int. That works... poorly if sizeof (int) < sizeof (void *)

I see (C99/C11 §6.3.2.3, #3). So the latter NULL definition only works poorly for variadic functions.

Is there any reason for an implementation to elect to use the non-casted version of NULL? It seems like an oversight.

Maybe arch with variable width pointer types like some embedded platforms?

How is integer zero better in that scenario, though? The (void-star)0 pointer can still be cast to the correct type (and will be for everything except variadic functions like printf).

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