[patch] Add a section about implementation-defined behavior to the user's manual

[Richard Smith]

On Tue, Jan 29, 2013 at 5:41 PM, Nico Weber <thakis at chromium.org> wrote:
> On Tue, Jan 29, 2013 at 5:39 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>> On Tue, Jan 29, 2013 at 4:47 PM, Nico Weber <thakis at chromium.org> wrote:
>>> On Tue, Jan 29, 2013 at 1:00 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>>>> On Tue, Jan 29, 2013 at 10:16 PM, Nico Weber <thakis at chromium.org> wrote:
>>>>> a coworker asked me if clang documents how it handles right shifts of
>>>>> signed numbers today. As far as I can tell there's no documentation
>>>>> for this, but I found PR11272 about documenting implementation-defined
>>>>> behavior. The bug suggests just linking to gcc's documentation as a
>>>>> first step, which is what the attached patch does. This isn't quite
>>>>> correct (for example, clang supports UCNs without any flags), but is
>>>>> correct for most things. People can fill in more details over time.
>>>>
>>>> +clang generally matches `gcc's implementation-defined
>>>> +behavior <http://gcc.gnu.org/onlinedocs/gcc-4.2.1/gcc/C-Implementation.html#C-Implementation>`.
>>>>
>>>> Maybe there's a different wording that does not promise too much?  I
>>>> can easily see users relying on this (or complaining about Clang's
>>>> implementation-defined behavior being different from gcc's).
>>>
>>> "generally tries to match"? The "generally" sounded fairly
>>> weasel-wordy to me already.
>>>
>>>> What might help is a list of implementation-defined behaviors with
>>>> quotations from the standard, as a boilerplate for developers to fill
>>>> in.  (It is much easier to write documentation when you know what
>>>> exactly you should describe.)
>>>
>>> I don't have a copy of the standard.
>>
>> Latest working draft in committee mailing:
>>
>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3485.pdf
>>
>> Current working draft:
>>
>> https://github.com/cplusplus/draft
>
> How similar is this to the list of implementation-defined behavior in
> the C standard?

Similar, not the same. C11 standard (minus cover sheet) is here:

http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf