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

[Christian Franke <Christian.Franke@t-online.de>]

Takashi Yano via Cygwin wrote:
> On Thu, 21 Sep 2023 21:06:59 +0200
> Christian Franke wrote:
>> ...
>> 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.
> Thanks for the pointer. I looked into the cygstdc++6.dll source code,
> and noticed that the code you mentioned is for glibc. In glibc,
> __newlocale() is defined and newlocale() is a weak alias for that.
>
> For generic libc (i.e. other than glibc), _S_create_c_locale() is
> defined as:
>
>    void
>    locale::facet::_S_create_c_locale(__c_locale& __cloc, const char* __s,
>                      __c_locale)
>    {
>      // Currently, the generic model only supports the "C" locale.
>      // See http://gcc.gnu.org/ml/libstdc++/2003-02/msg00345.html
>      __cloc = 0;
>      if (strcmp(__s, "C"))
>        __throw_runtime_error(__N("locale::facet::_S_create_c_locale "
>                  "name not valid"));
>    }
>
> in /libstdc++-v3/config/locale/generic/c_locale.cc.

Thanks for clarification. Same applies to MinGW-w64 runtime.

The reason why cygstdc++-6.dll imports newlocale() and other *locale() 
from cygwin1.dll are only the C++17 std::from_chars() functions 
(src/c++17/floating_from_chars.cc). These switch temporarily to "C" 
locale. MinGW-w64 does not support these.

-- 
Regards,
Christian