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.
