Re: [PATCH 1/7] Rework strbuf API and semantics.

From: David Kastrup <dak@gnu.org>
Date: Sep 6, 2007, 15:53 UTC
Message-ID: <85hcm7bxjl.fsf@lola.goethe.zz>
In-Reply-To: <20070906153613.GA4008@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 19 quoted lines

> On Thu, Sep 06, 2007 at 05:06:52PM +0200, David Kastrup wrote:
>
>> >   If an object that has automatic storage duration is not initialized
>> >   explicitly, its value is indeterminate. If an object that has static
>> >   storage duration is not initialized explicitly, then:
>> >
>> >   -- if it has pointer type, it is initialized to a null pointer;
>> 
>> That's actually a new one to me.  I don't think that it has been
>> always the case in ANSI C.
>
> I don't have the C89 standard, so it's hard to be authoritative.
> However, according to TCOR1 to the C89 standard, the original text of
> 6.5.7 contained:
>
>   If an object that has static storage duration is not initialized
>   explicitly, it is initialized implicitly as if every member that has
>   arithmetic type were assigned 0 and every member that has pointer type
>   were assigned a null pointer constant.

Maybe I am confusing this with the effects of calloc or memset(...,0).

> But for the case of pointer initializations, both have the same
> effect.  So I think it has always been the case. Pre-ANSI, who
> knows. :)

In the original K&R C, a null pointer likely could have been assumed to have zero bits throughout. The non-zero-bits NULL pointer concept just reeks of standard committees... So maybe this never had been an issue, for different reasons.

> And now I must go get some real work done instead of snooping
> through standards. :)

Sorry for the diversion.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum