https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86742
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- en.cppreference.com is not our documentation. Our documentation clearly says this isn't implemented yet, see https://gcc.gnu.org/gcc-8/changes.html#libstdcxx and https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2017 C++17 support is documented as incomplete, specifically std::to_chars for floating point types isn't available.
