Function utf16to8

third-party/utf8cpp/source/utf8/cpp17.h:42–47

    }

    inline std::string utf16to8(std::u16string_view s)
    {
        std::string result;
        utf16to8(s.begin(), s.end(), std::back_inserter(result));
        return result;
    }

    inline std::u16string utf8to16(std::string_view s)
    {