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

[redi at gcc dot gnu.org]

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

--- Comment #30 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Correct, that's how std::from_chars works. It never parses a prefix, and you
need to use the hex format if you want to parse hex floats. There is no bug
with from_chars, and it's nothing to do with this bug report for istream.

https://eel.is/c++draft/text#charconv.from.chars-6.4