Signedness of wchar_t and wint_t leads to problems with gcc -Wsign-conversion

[Michael Kerrisk (man-pages)]

On 11/21/2016 02:28 PM, Andreas Schwab wrote:
> On Nov 21 2016, "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> wrote:
> 
>> On 11/21/2016 02:01 PM, Andreas Schwab wrote:
>>> On Nov 21 2016, "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> wrote:
>>>
>>>> So, I'm not quite clear on the point that you are making in your
>>>> second point. Given code such as:
>>>>
>>>>     wchar_t w;
>>>>     ...
>>>>     if (iswlower((wint_t) w) ....
>>>>
>>>> Do you mean that the standards are saying that casting to wint_t here
>>>> is guaranteed to be correct? I can't see the line of reasoning that
>>>> leads there.
>>>
>>> Any valid value of wchar_t is representable by wint_t.  I cannot find
>>> any more convincing argument.
>>
>> Yes, but is a sign-extended wchar_t a valid value?
> 
> A valid value of wchar_t is a valid value.

Sorry, that makes me no wiser :-(. You snipped the question
whose answer might help me:

To put things another way, why is this scenario different from
the islower() example, where the cast to '(unsigned char)' is
needed in portable code?

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/