namespace std {
  // floating-point format for primitive numerical conversion
  enum class chars_format {
    scientific = /* unspecified */,
    fixed = /* unspecified */,
    hex = /* unspecified */,
    general = fixed | scientific
  };
 
 
  // primitive numerical output conversion
  struct to_chars_result {
    char* ptr;
    errc ec;
    friend bool operator==(const to_chars_result&, const to_chars_result&) = default;
  };
 
  constexpr
  to_chars_result to_chars(char* first, char* last,
                           /* integer-type */ value, int base = 10);
  to_chars_result to_chars(char* first, char* last, bool value, int base = 10) = delete;
  to_chars_result to_chars(char* first, char* last, /* floating-point-type */ value);
  to_chars_result to_chars(char* first, char* last, /* floating-point-type */ value,
                           chars_format fmt);
  to_chars_result to_chars(char* first, char* last, /* floating-point-type */ value,
                           chars_format fmt, int precision);
 
  // primitive numerical input conversion
  struct from_chars_result {
    const char* ptr;
    errc ec;
    friend bool operator==(const from_chars_result&, const from_chars_result&) = default;
  };
 
  constexpr
  from_chars_result from_chars(const char* first, const char* last,
                               /* integer-type */& value, int base = 10);
  from_chars_result from_chars(const char* first, const char* last,
                               /* floating-point-type */& value,
                               chars_format fmt = chars_format::general);
}