https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109162
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #3) > (In reply to Jonathan Wakely from comment #0) > > https://wg21.link/P2419R2 localized chrono formatting (also p2372r3) > > I think this this requires using nl_langinfo_l(CODESET, loc) to find out if > the locale uses UTF-8, and then use iconv to convert to UTF-8 if it doesn't. > But I'm not sure how we do that for an arbitrary std::locale which doesn't > have an associated C locale, and we can't get its locale_t identifier anyway. I remain confused about how to implement this. We could use newlocale(loc.name()) to try to open a C locale from the C++ locale's name, and if that works use nl_langinfo_l to get the locale's encoding, then use iconv to convert to UTF-8. Libc++ doesn't implement this yet. {fmt} does ... but it seems broken. It uses std::codecvt<char32_t, char, mbstate_t> to convert the locale's encoding to UTF-32 and then converts that to UTF-8. But that's wrong. That codecvt specialization converts between UTF-8 and UTF-32, it's locale-independent. So the example in P2419 fails with a format_error exception when I run it: #include <locale> #include <print> #include <chrono> #include <iostream> #include <fmt/format.h> #include <fmt/chrono.h> int main() { std::locale::global(std::locale("ru_UA.koi8u")); std::string s = fmt::format("День недели: {:L}", std::chrono::Monday); std::cout << s << '\n'; } terminate called after throwing an instance of 'fmt::v9::format_error' what(): failed to format time Aborted (core dumped)
