27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.3 Class day [time.cal.day]

27.8.3.1 Overview [time.cal.day.overview]

namespace std::chrono {
  class day {
    unsigned char d_;           // exposition only
  public:
    day() = default;
    constexpr explicit day(unsigned d) noexcept;

    constexpr day& operator++()    noexcept;
    constexpr day  operator++(int) noexcept;
    constexpr day& operator--()    noexcept;
    constexpr day  operator--(int) noexcept;

    constexpr day& operator+=(const days& d) noexcept;
    constexpr day& operator-=(const days& d) noexcept;

    constexpr explicit operator unsigned() const noexcept;
    constexpr bool ok() const noexcept;
  };
}