Re: Remaining dependency on setlocale()

On Mon, 2025-07-07 at 17:56 -0700, Jeff Davis wrote:
> I looked into this a bit, and if I understand correctly, the only
> problem is with strerror() and strerror_r(), which depend on
> LC_MESSAGES for the language but LC_CTYPE to find the right encoding.

...

> Windows would be a different story, though: strerror() doesn't seem
> to
> have a variant that accepts a _locale_t object, and even if it did, I
> don't see a way to create a _locale_t object with LC_MESSAGES and
> LC_CTYPE set to different values.

I think I have an answer to the second part here:

"For information about the format of the locale argument, see Locale
names, Languages, and Country/Region strings."

https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/create-locale-wcreate-locale?view=msvc-170

and when I follow that link, I see:

  "You can specify multiple category types, separated by semicolons.
Category types that aren't specified use the current locale setting.
For example, this code snippet sets the current locale for all
categories to de-DE, and then sets the categories LC_MONETARY to en-GB
and LC_TIME to es-ES:

  _wsetlocale(LC_ALL, L"de-DE");
  _wsetlocale(LC_ALL, L"LC_MONETARY=en-GB;LC_TIME=es-ES");"

https://learn.microsoft.com/en-us/cpp/c-runtime-library/locale-names-languages-and-country-region-strings?view=msvc-170

So we just need to construct a string of the right form, and we can
have a _locale_t object representing the global locale for all
categories. I'm not sure exactly how we escape the individual locale
names, but it might be enough to just reject ';' in the locale name (at
least for windows).

The first problem -- how to affect the encoding of strings returned by
strerror() on windows -- may be solvable as well. It looks like
LC_MESSAGES is not supported at all on windows, so the only thing to be
concerned about is the encoding, which is affected by LC_CTYPE. But
windows doesn't offer uselocale() or strerror_l(). The only way seems
to be to call _configthreadlocale(_ENABLE_PER_THREAD_LOCALE) and then
setlocale(LC_CTYPE, datctype) right before strerror(), and switch it
back to "C" right afterward. Comments welcome.

Regards,
    Jeff Davis