27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.16 Class year_­month_­weekday [time.cal.ymwd]

27.8.16.1 Overview [time.cal.ymwd.overview]

namespace std::chrono {
  class year_month_weekday {
    chrono::year            y_;         // exposition only
    chrono::month           m_;         // exposition only
    chrono::weekday_indexed wdi_;       // exposition only

  public:
    year_month_weekday() = default;
    constexpr year_month_weekday(const chrono::year& y, const chrono::month& m,
                                 const chrono::weekday_indexed& wdi) noexcept;
    constexpr year_month_weekday(const sys_days& dp) noexcept;
    constexpr explicit year_month_weekday(const local_days& dp) noexcept;

    constexpr year_month_weekday& operator+=(const months& m) noexcept;
    constexpr year_month_weekday& operator-=(const months& m) noexcept;
    constexpr year_month_weekday& operator+=(const years& y)  noexcept;
    constexpr year_month_weekday& operator-=(const years& y)  noexcept;

    constexpr chrono::year            year()            const noexcept;
    constexpr chrono::month           month()           const noexcept;
    constexpr chrono::weekday         weekday()         const noexcept;
    constexpr unsigned                index()           const noexcept;
    constexpr chrono::weekday_indexed weekday_indexed() const noexcept;

    constexpr          operator sys_days()   const noexcept;
    constexpr explicit operator local_days() const noexcept;
    constexpr bool ok() const noexcept;
  };
}
year_­month_­weekday represents a specific year, month, and weekday of the month.
year_­month_­weekday is a field-based time point with a resolution of days.
Note
:
year_­month_­weekday 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_­weekday meets the Cpp17EqualityComparable (Table 23) requirements.
year_­month_­weekday is a trivially copyable and standard-layout class type.

27.8.16.2 Member functions [time.cal.ymwd.members]

constexpr year_month_weekday(const chrono::year& y, const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept;
Effects: Initializes y_­ with y, m_­ with m, and wdi_­ with wdi.
constexpr year_month_weekday(const sys_days& dp) noexcept;
Effects: Constructs an object of type year_­month_­weekday which corresponds to the date represented by dp.
Remarks: For any value ymdl of type year_­month_­weekday for which ymdl.ok() is true, ymdl == year_­month_­weekday{sys_­days{ymdl}} is true.
constexpr explicit year_month_weekday(const local_days& dp) noexcept;
Effects: Equivalent to constructing with sys_­days{dp.time_­since_­epoch()}.
constexpr year_month_weekday& operator+=(const months& m) noexcept;
Effects: *this = *this + m.
Returns: *this.
constexpr year_month_weekday& operator-=(const months& m) noexcept;
Effects: *this = *this - m.
Returns: *this.
constexpr year_month_weekday& operator+=(const years& y) noexcept;
Effects: *this = *this + y.
Returns: *this.
constexpr year_month_weekday& 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::weekday weekday() const noexcept;
Returns: wdi_­.weekday().
constexpr unsigned index() const noexcept;
Returns: wdi_­.index().
constexpr chrono::weekday_indexed weekday_indexed() const noexcept;
Returns: wdi_­.
constexpr operator sys_days() const noexcept;
Returns: If y_­.ok() && m_­.ok() && wdi_­.weekday().ok(), returns a sys_­days that represents the date (index() - 1) * 7 days after the first weekday() of year()/month().
If index() is 0 the returned sys_­days represents the date 7 days prior to the first weekday() of year()/month().
Otherwise the returned value is unspecified.
constexpr explicit operator local_days() const noexcept;
Returns: local_­days{sys_­days{*this}.time_­since_­epoch()}.
constexpr bool ok() const noexcept;
Returns: If any of y_­.ok(), m_­.ok(), or wdi_­.ok() is false, returns false.
Otherwise, if *this represents a valid date, returns true.
Otherwise, returns false.

27.8.16.3 Non-member functions [time.cal.ymwd.nonmembers]

constexpr bool operator==(const year_month_weekday& x, const year_month_weekday& y) noexcept;
Returns:
x.year() == y.year() && x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed()
constexpr year_month_weekday operator+(const year_month_weekday& ymwd, const months& dm) noexcept;
Returns: (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_­indexed().
constexpr year_month_weekday operator+(const months& dm, const year_month_weekday& ymwd) noexcept;
Returns: ymwd + dm.
constexpr year_month_weekday operator-(const year_month_weekday& ymwd, const months& dm) noexcept;
Returns: ymwd + (-dm).
constexpr year_month_weekday operator+(const year_month_weekday& ymwd, const years& dy) noexcept;
Returns: {ymwd.year()+dy, ymwd.month(), ymwd.weekday_­indexed()}.
constexpr year_month_weekday operator+(const years& dy, const year_month_weekday& ymwd) noexcept;
Returns: ymwd + dy.
constexpr year_month_weekday operator-(const year_month_weekday& ymwd, const years& dy) noexcept;
Returns: ymwd + (-dy).
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const year_month_weekday& ymwd);
Effects: Equivalent to:
return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{}/{}"),
                    ymwd.year(), ymwd.month(), ymwd.weekday_indexed());