29 Time library [time]

29.8 The civil calendar [time.cal]

29.8.14 Class year_month_day [time.cal.ymd]

29.8.14.2 Member functions [time.cal.ymd.members]

constexpr year_month_day(const chrono::year& y, const chrono::month& m, const chrono::day& d) noexcept;
Effects: Initializes y_ with y, m_ with m, and d_ with d.
constexpr year_month_day(const year_month_day_last& ymdl) noexcept;
Effects: Initializes y_ with ymdl.year(), m_ with ymdl.month(), and d_ with ymdl.day().
[Note 1: 
This conversion from year_month_day_last to year_month_day can be more efficient than converting a year_month_day_last to a sys_days, and then converting that sys_days to a year_month_day.
— end note]
constexpr year_month_day(const sys_days& dp) noexcept;
Effects: Constructs an object of type year_month_day that corresponds to the date represented by dp.
Remarks: For any value ymd of type year_month_day for which ymd.ok() is true, ymd == year_month_day{sys_days{ymd}} is true.
constexpr explicit year_month_day(const local_days& dp) noexcept;
Effects: Equivalent to constructing with sys_days{dp.time_since_epoch()}.
constexpr year_month_day& operator+=(const months& m) noexcept;
Constraints: If the argument supplied by the caller for the months parameter is convertible to years, its implicit conversion sequence to years is worse than its implicit conversion sequence to months ([over.ics.rank]).
Effects: *this = *this + m.
Returns: *this.
constexpr year_month_day& operator-=(const months& m) noexcept;
Constraints: If the argument supplied by the caller for the months parameter is convertible to years, its implicit conversion sequence to years is worse than its implicit conversion sequence to months ([over.ics.rank]).
Effects: *this = *this - m.
Returns: *this.
constexpr year_month_day& year_month_day::operator+=(const years& y) noexcept;
Effects: *this = *this + y.
Returns: *this.
constexpr year_month_day& year_month_day::operator-=(const years& y) noexcept;
Effects: *this = *this - y.
Returns: *this.
constexpr chrono::year year() const noexcept;
Returns: y_.
constexpr chrono::month month() const noexcept;
Returns: m_.
constexpr chrono::day day() const noexcept;
Returns: d_.
constexpr operator sys_days() const noexcept;
Returns: If ok(), returns a sys_days holding a count of days from the sys_days epoch to *this (a negative value if *this represents a date prior to the sys_days epoch).
Otherwise, if y_.ok() && m_.ok() is true, returns sys_days{y_/m_/1d} + (d_ - 1d).
Otherwise the value returned is unspecified.
Remarks: A sys_days in the range [days{-12687428}, days{11248737}] which is converted to a year_month_day has the same value when converted back to a sys_days.
[Example 1: static_assert(year_month_day{sys_days{2017y/January/0}} == 2016y/December/31); static_assert(year_month_day{sys_days{2017y/January/31}} == 2017y/January/31); static_assert(year_month_day{sys_days{2017y/January/32}} == 2017y/February/1); — end example]
constexpr explicit operator local_days() const noexcept;
Returns: local_days{sys_days{*this}.time_since_epoch()}.
constexpr bool ok() const noexcept;
Returns: If y_.ok() is true, and m_.ok() is true, and d_ is in the range [1d, (y_/m_/last).day()], then returns true; otherwise returns false.