https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117135
--- Comment #2 from Christophe Lyon <clyon at gcc dot gnu.org> --- The additional debug output with your patch is: Wide D_T_FMT for C locale: eofbit: 0 failbit: 0 badbit: 0 22_locale/time_get/get/wchar_t/5.cc:29: int main(): Assertion 'err == std::ios::eofbit' failed.