29 Time library [time]

29.8 The civil calendar [time.cal]

29.8.14 Class year_month_day [time.cal.ymd] Overview [time.cal.ymd.overview]

namespace std::chrono { class year_month_day { chrono::year y_; // exposition only chrono::month m_; // exposition only chrono::day d_; // exposition only public: year_month_day() = default; constexpr year_month_day(const chrono::year& y, const chrono::month& m, const chrono::day& d) noexcept; constexpr year_month_day(const year_month_day_last& ymdl) noexcept; constexpr year_month_day(const sys_days& dp) noexcept; constexpr explicit year_month_day(const local_days& dp) noexcept; constexpr year_month_day& operator+=(const months& m) noexcept; constexpr year_month_day& operator-=(const months& m) noexcept; constexpr year_month_day& operator+=(const years& y) noexcept; constexpr year_month_day& operator-=(const years& y) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::day day() const noexcept; constexpr operator sys_days() const noexcept; constexpr explicit operator local_days() const noexcept; constexpr bool ok() const noexcept; }; }
year_month_day represents a specific year, month, and day.
year_month_day is a field-based time point with a resolution of days.
[Note 1: 
year_month_day supports years- and months-oriented arithmetic, but not days-oriented arithmetic.
For the latter, there is a conversion to sys_days, which efficiently supports days-oriented arithmetic.
— end note]
year_month_day meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements.
year_month_day is a trivially copyable and standard-layout class type.