Re: What's in git.git

On Mon, 26 Jun 2006, Junio C Hamano wrote:

As long as none of the following does not dereference the NULL
pointer that should work fine:

	- memchr(NULL, ch, 0);

        - memcmp(NULL, ptr, 0);

        - stream.next_in = NULL;
          stream.avail_in = 0;
          deflate(&stream, Z_FINISH);

Well, they clearly _shouldn't_, but bugs happen in libraries too.

(The reason they shouldn't is simple: replace the NULL pointer with a 
perfectly normal pointer at the end of a page, and if you access past the 
length of the memory area, you'd get the same SIGSEGV that a NULL pointer 
should give you).

So the question is how much to trust the libraries for a special case that 
has a clearly "Right Answer", but is probably unusual in practice.

(That said, "malloc(0)" can validly return NULL, so the NULL+<zero length> 
thing can really happen in real code even if it's not explicit).

If people want to be anally defensive, we should give it a valid pointer. 
If there are known buggy libraries, I wouldn't object to something 
explicit like

	#define DUMMYPTR ((void *)"")

and hide it that way - the code may be the exact same thing that I 
objected to, but now you're showing that you know that the cast is crud, 
and you're just wanting to pass in some non-NULL valid pointer that can be 
dereferenced but never written to.

Personally, I think NULL is much better, until somebody shows an actual 
buggy library.

			Linus