Re: std::runtime_error on std::locale("")

[Martin Wege <martin.l.wege@gmail.com>]

On Thu, Sep 21, 2023 at 9:07 PM Christian Franke via Cygwin
<cygwin@cygwin.com> wrote:
>
> Brian Inglis via Cygwin wrote:
> > On 2023-09-21 10:28, Takashi Yano via Cygwin wrote:
> >> On Fri, 22 Sep 2023 01:12:04 +0900
> >> Takashi Yano wrote:
> >>> I wonder why the following code throws std::runtime_error
> >>> even though the LC_ALL is set to valid locale other than "C".
> >>> This does not occur only when LC_ALL is set to "C".
> >>>
> >>> #include <locale>
> >>> int main()
> >>> {
> >>>     std::locale("");
> >>>     return 0;
> >>> }
> >>>
> >>> In linux, this occurs only when the LC_ALL is set to invalid
> >>> locale (i.e. locale that is not registered in system).
> >>
> >> Similarly,
> >> std::locale("ja_JP.UTF-8")
> >> throws std::runtime_error in cygwin.
> >
> > Looks like the implementation does not like any default "" or explicit
> > "en_US.UTF-8" strings there! See example at link and below; results
> > are always the same:
> >
> >     https://en.cppreference.com/w/cpp/locale/locale
> >
> > #include <iostream>
> > #include <locale>
> >
> > int main()
> > {
> >     std::wcout << "User-preferred locale setting is "
> >            << std::locale().name().c_str() << '\n';
> >
> >     // on startup, the global locale is the "C" locale
> >     std::wcout << 1000.01 << '\n';
> >
> >     // replace the C++ global locale and the "C" locale with the
> > user-preferred locale
> >     std::locale::global(std::locale(""));
> >     // use the new global locale for future wide character output
> >     std::wcout.imbue(std::locale());
> >
> >     // output the same number again
> >     std::wcout << 1000.01 << '\n';
> > }
> >
> > $ g++ -o c++locale{,.cc}
> > $ ./c++locale
> > User-preferred locale setting is C
> > 1000.01
> > terminate called after throwing an instance of 'std::runtime_error'
> >   what():  locale::facet::_S_create_c_locale name not valid
> > Aborted (core dumped)
> >
>
> According to libstdc++ source, the internal function
> locale::facet::_S_create_c_locale() calls some __newlocale() which
> apparently does not arrive at newlocale() from cygwin1.dll. But
> cygstdc++-6.dll imports newlocale() from cygwin1.dll.

So this is a BUG?

>
> Only standard locale "C" and its alias "POSIX" work with C++ std::locale().
>
> The cygwin1.dll function newlocale() works as expected - except that it
> does not set errno if the locale name is invalid.

What does
bash -c 'locale -a'
print on your system?

Thanks,
Martin