https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85098
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- Untested fix: --- a/libstdc++-v3/include/bits/regex.h +++ b/libstdc++-v3/include/bits/regex.h @@ -776,6 +776,37 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _AutomatonPtr _M_automaton; }; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::icase; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::nosubs; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::optimize; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::collate; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::ECMAScript; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::basic; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::extended; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::awk; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::grep; + template<typename _Ch, typename _Tr> + constexpr regex_constants::syntax_option_type + basic_regex<_Ch, _Tr>::egrep; + #if __cpp_deduction_guides >= 201606 template<typename _ForwardIterator> basic_regex(_ForwardIterator, _ForwardIterator,