26 Time library [time]

26.8 The civil calendar [time.cal]

26.8.3 Class day [time.cal.day]

26.8.3.2 Member functions [time.cal.day.members]

constexpr explicit day(unsigned d) noexcept;
Effects: Constructs an object of type day by initializing d_­ with d.
The value held is unspecified if d is not in the range [0, 255].
constexpr day& operator++() noexcept;
Effects: ++d_­.
Returns: *this.
constexpr day operator++(int) noexcept;
Effects: ++(*this).
Returns: A copy of *this as it existed on entry to this member function.
constexpr day& operator--() noexcept;
Effects: --d_­.
Returns: *this.
constexpr day operator--(int) noexcept;
Effects: --(*this).
Returns: A copy of *this as it existed on entry to this member function.
constexpr day& operator+=(const days& d) noexcept;
Effects: *this = *this + d.
Returns: *this.
constexpr day& operator-=(const days& d) noexcept;
Effects: *this = *this - d.
Returns: *this.
constexpr explicit operator unsigned() const noexcept;
Returns: d_­.
constexpr bool ok() const noexcept;
Returns: 1 <= d_­ && d_­ <= 31.