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Date: Wed, 1 Jun 2011 19:25:03 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Steve Kargl <sgk@troutmask.apl.washington.edu>
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Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org, Pawel Jakub Dawidek <pjd@FreeBSD.org>,
	Ben Laurie <ben@links.org>
Subject: Re: svn commit: r222084 - head/contrib/gperf/src
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On Tue, 31 May 2011, Steve Kargl wrote:

> On Tue, May 31, 2011 at 03:28:45PM +0100, Ben Laurie wrote:
>> On 18/05/2011 22:16, Pawel Jakub Dawidek wrote:
>>> On Wed, May 18, 2011 at 09:06:20PM +0000, Ben Laurie wrote:
>>>> Author: benl
>>>> Date: Wed May 18 21:06:20 2011
>>>> New Revision: 222084
>>>> URL: http://svn.freebsd.org/changeset/base/222084
>>>>
>>>> Log:
>>>>   Fix clang warnings.
>>>>
>>>>   Approved by:	philip (mentor)
>>> [...]
>>>> -            fprintf (stderr, " by changing asso_value['%c'] (char #%d) to %d\n",
>>>> +            fprintf (stderr, " by changing asso_value['%c'] (char #%zd) to %d\n",
>>>>                       *p, p - union_set + 1, asso_values[(unsigned char)(*p)]);
>>>
>>> Hmm, both 'p' and 'union_set' are 'char *' and %zd is for ssize_t. It is
>>> a bit strange that it fixes the warning.
>>
>> Why? The difference between two pointers is ssize_t, surely?
>>
>
>> From n1256.pdf,
>
>  When two pointers are subtracted, both shall point to elements of
>  the same array object, or one past the last element of the array
>  object; the result is the difference of the subscripts of the two
>  array elements.  The size of the result is implementation-defined,
>  and its type (a signed integer type) is ptrdiff_t defined in the
>  <stddef.h> header.
>
> ptrdiff_t is not necessarily that same as ssize_t.

ssize_t doesn't even exist in Standard C.  It is a POSIX thing, mainly
for the (broken for historical reasons) return type of read(2) and
similar functions.

Bruce