Re: [PATCH 1/3] diff --stat: allow custom diffstat output width.

From: Linus Torvalds <torvalds@osdl.org>
Date: Sep 29, 2006, 06:17 UTC
Message-ID: <Pine.LNX.4.64.0609282307220.3952@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.64.0609282252430.3952@g5.osdl.org>

On Thu, 28 Sep 2006, Linus Torvalds wrote:

Show 5 quoted lines

> 
> because the only reason strtoul() warns now is that C type-rules don't 
> allow the (obviously safe - but pointers migth have strange 
> representations) conversion of "char **" into "const char **", even though 
> "char *" can be converted into "const char *".

I phrased that badly.

IF C pointer conversion allowed implicit addition of "const" past the top-most level, ANSI C would have just done "strtoul()" as

	unsigned long strtoul(const char *n, const char **p, int);

ie they could just have added the "const" not just to the first argument, and legact programs (without const) would still have worked fine.

But _because_ that's not how C type rules work, we have the current situation where the first argument is a "const char *", and the second argument _logically_ should be a pointer to such an entity, but because that would have caused bogus warnings for any code that just used a regular "char **" without any const at all, that wasn't an option.

So that explains why ANSI C has insane imbalances like this. It's easy to add a "const" to a _first-level_ pointer to say "we allow both const and regular pointers to this thing", but sadly you can't do it for a pointer to such a pointer.

			Linus