From: Alejandro Colomar <alx.manpages@gmail.com>
To: Martin Uecker <uecker@tugraz.at>, Joseph Myers <joseph@codesourcery.com>
Cc: Ingo Schwarze <schwarze@usta.de>,
JeanHeyd Meneide <wg14@soasis.org>,
linux-man@vger.kernel.org, gcc@gcc.gnu.org
Subject: Re: [PATCH] Various pages: SYNOPSIS: Use VLA syntax in function parameters
Date: Sun, 13 Nov 2022 15:02:40 +0100 [thread overview]
Message-ID: <31e1cf34-b42f-24c5-2109-f8214c28af3e@gmail.com> (raw)
In-Reply-To: <792055f0-114d-d4bc-52f0-c242d1767c0b@gmail.com>
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On 11/13/22 14:33, Alejandro Colomar wrote:
> Hi Martin,
>
> On 11/13/22 14:19, Alejandro Colomar wrote:
>>> But there are not only syntactical problems, because
>>> also the type of the parameter might become relevant
>>> and then you can get circular dependencies:
>>>
>>> void foo(char (*a)[sizeof *.b], char (*b)[sizeof *.a]);
>>
>> This seems to be a difficult stone in the road.
>>
>>>
>>> I am not sure what would the best way to fix it. One
>>> could specifiy that parameters referred to by
>>> the .identifer syntax must of some integer type and
>>> that the sub-expression .identifer is always
>>> converted to a 'size_t'.
>>
>> That makes sense, but then overnight some quite useful thing came to my mind
>> that would not be possible with this limitation:
>>
>>
>> <https://software.codidact.com/posts/285946>
>>
>> char *
>> stpecpy(char dst[.end - .dst], char *src, char end[1])
Heh, I got an off-by-one error. It should be dst[.end - .dst + 1], of course,
and then the result of the whole expression would be 0, which is fine as size_t.
So, never mind.
>> {
>> for (/* void */; dst <= end; dst++) {
>> *dst = *src++;
>> if (*dst == '\0')
>> return dst;
>> }
>> /* Truncation detected */
>> *end = '\0';
>>
>> #if !defined(NDEBUG)
>> /* Consume the rest of the input string. */
>> while (*src++) {};
>> #endif
>>
>> return end + 1;
>> }
>
> And I forgot to say it: Default promotions rank high (probably the highest) in
> my list of most hated features^Wbugs in C. I wouldn't convert it to size_t, but
> rather follow normal promotion rules.
>
> Since you can use anything between INTMAX_MIN and UINTMAX_MAX for accessing an
> array (which took me some time to understand), I'd also allow the same here. So,
> the type of the expression between [] could perfectly be signed or unsigned.
>
> So, you could use size_t for very high indices, or e.g. ptrdiff_t if you want to
> allow negative numbers. In the function above, since dst can be a pointer to
> one-past-the-end (it represents a previous truncation; that's why the test
> dst<=end), forcing a size_t conversion would disallow that syntax.
>
> Cheers,
>
> Alex
>
--
<http://www.alejandro-colomar.es/>
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next prev parent reply other threads:[~2022-11-13 14:02 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220826210710.35237-1-alx.manpages@gmail.com>
[not found] ` <Ywn7jMtB5ppSW0PB@asta-kit.de>
[not found] ` <89d79095-d1cd-ab2b-00e4-caa31126751e@gmail.com>
[not found] ` <YwoXTGD8ljB8Gg6s@asta-kit.de>
[not found] ` <e29de088-ae10-bbc8-0bfd-90bbb63aaf06@gmail.com>
[not found] ` <5ba53bad-019e-8a94-d61e-85b2f13223a9@gmail.com>
[not found] ` <CACqA6+mfaj6Viw+LVOG=nE350gQhCwVKXRzycVru5Oi4EJzgTg@mail.gmail.com>
[not found] ` <491a930d-47eb-7c86-c0c4-25eef4ac0be0@gmail.com>
2022-09-02 21:57 ` Alejandro Colomar
2022-09-03 12:47 ` Martin Uecker
2022-09-03 13:29 ` Ingo Schwarze
2022-09-03 15:08 ` Alejandro Colomar
2022-09-03 13:41 ` Alejandro Colomar
2022-09-03 14:35 ` Martin Uecker
2022-09-03 14:59 ` Alejandro Colomar
2022-09-03 15:31 ` Martin Uecker
2022-09-03 20:02 ` Alejandro Colomar
2022-09-05 14:31 ` Alejandro Colomar
2022-11-10 0:06 ` Alejandro Colomar
2022-11-10 0:09 ` Alejandro Colomar
2022-11-10 1:33 ` Joseph Myers
2022-11-10 1:39 ` Joseph Myers
2022-11-10 6:21 ` Martin Uecker
2022-11-10 10:09 ` Alejandro Colomar
2022-11-10 23:19 ` Joseph Myers
2022-11-10 23:28 ` Alejandro Colomar
2022-11-11 19:52 ` Martin Uecker
2022-11-12 1:09 ` Joseph Myers
2022-11-12 7:24 ` Martin Uecker
2022-11-12 12:34 ` Alejandro Colomar
2022-11-12 12:46 ` Alejandro Colomar
2022-11-12 13:03 ` Joseph Myers
2022-11-12 13:40 ` Alejandro Colomar
2022-11-12 13:58 ` Alejandro Colomar
2022-11-12 14:54 ` Joseph Myers
2022-11-12 15:35 ` Alejandro Colomar
2022-11-12 17:02 ` Joseph Myers
2022-11-12 17:08 ` Alejandro Colomar
2022-11-12 15:56 ` Martin Uecker
2022-11-13 13:19 ` Alejandro Colomar
2022-11-13 13:33 ` Alejandro Colomar
2022-11-13 14:02 ` Alejandro Colomar [this message]
2022-11-13 14:58 ` Martin Uecker
2022-11-13 15:15 ` Alejandro Colomar
2022-11-13 15:32 ` Martin Uecker
2022-11-13 16:25 ` Alejandro Colomar
2022-11-13 16:28 ` Alejandro Colomar
2022-11-13 16:31 ` Alejandro Colomar
2022-11-13 16:34 ` Alejandro Colomar
2022-11-13 16:56 ` Alejandro Colomar
2022-11-13 19:05 ` Alejandro Colomar
2022-11-14 18:13 ` Joseph Myers
2022-11-28 22:59 ` Alex Colomar
2022-11-28 23:18 ` Alex Colomar
2022-11-29 0:05 ` Joseph Myers
2022-11-29 14:58 ` Michael Matz
2022-11-29 15:17 ` Uecker, Martin
2022-11-29 15:44 ` Michael Matz
2022-11-29 16:58 ` Uecker, Martin
2022-11-29 17:28 ` Alex Colomar
2022-11-29 16:49 ` Joseph Myers
2022-11-29 16:53 ` Jonathan Wakely
2022-11-29 17:00 ` Martin Uecker
2022-11-29 17:19 ` Alex Colomar
2022-11-29 17:29 ` Alex Colomar
2022-12-03 21:03 ` Alejandro Colomar
2022-12-03 21:13 ` Andrew Pinski
2022-12-03 21:15 ` Martin Uecker
2022-12-03 21:18 ` Alejandro Colomar
2022-12-06 2:08 ` Joseph Myers
2022-11-14 17:52 ` Joseph Myers
2022-11-14 17:57 ` Alejandro Colomar
2022-11-14 18:26 ` Joseph Myers
2022-11-28 23:02 ` Alex Colomar
2022-11-10 9:40 ` G. Branden Robinson
2022-11-10 10:59 ` Alejandro Colomar
2022-11-10 22:25 ` G. Branden Robinson
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