[:xdigit:] does not work with std::wstring in a Cygwin environment

[Achim Gratz]

Gans, Markus writes:
> This seems to be an internal Cygwin error:
>
> https://www.reddit.com/r/cpp_questions/comments/sp52gq/xdigit_does_not_work_with_stdwstring_in_a_cygwin/
[…]
> Question: Why does Cygwin not detect the letters a, b, c, d, e, and f as hexadecimal digits in a wide string?

I have no idea, there doesn't seem to be any external libraries
involved.  At a quick glance there also weren't any commits that would
obviously fix a bug in that region.  There is no OS specific
configuration for Cygwin explicitly, instead there is one for newlib
that actually gets used.

Please report this bug upstream.


Regards,
Achim.
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