[Bug libstdc++/81122] [DR 2381] parsing f stopped after '0' when reading std::hexfloat >> f;

[terra at gnome dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81122

--- Comment #31 from M Welinder <terra at gnome dot org> ---
I see.  That is interestingly different from what
https://en.cppreference.com/w/cpp/utility/from_chars.html says.  paraphrased:
same as strtod, but 0x not allowed when hex format is explicitly specified.