27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.14 Class year_­month_­day [time.cal.ymd]

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

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constexpr year_month_day(const chrono::year& y, const chrono::month& m, const chrono::day& d) noexcept;
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#
Effects: Initializes y_­ with y, m_­ with m, and d_­ with d.
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constexpr year_month_day(const year_month_day_last& ymdl) noexcept;
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Effects: Initializes y_­ with ymdl.year(), m_­ with ymdl.month(), and d_­ with ymdl.day().
[Note
:
This conversion from year_­month_­day_­last to year_­month_­day may 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
]
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constexpr year_month_day(const sys_days& dp) noexcept;
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Effects: Constructs an object of type year_­month_­day that corresponds to the date represented by dp.
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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.
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constexpr explicit year_month_day(const local_days& dp) noexcept;
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Effects: Equivalent to constructing with sys_­days{dp.time_­since_­epoch()}.
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constexpr year_month_day& operator+=(const months& m) noexcept;
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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]).
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Effects: *this = *this + m.
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Returns: *this.
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constexpr year_month_day& operator-=(const months& m) noexcept;
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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]).
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Effects: *this = *this - m.
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Returns: *this.
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constexpr year_month_day& year_month_day::operator+=(const years& y) noexcept;
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Effects: *this = *this + y.
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Returns: *this.
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constexpr year_month_day& year_month_day::operator-=(const years& y) noexcept;
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Effects: *this = *this - y.
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Returns: *this.
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constexpr chrono::year year() const noexcept;
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Returns: y_­.
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constexpr chrono::month month() const noexcept;
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Returns: m_­.
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constexpr chrono::day day() const noexcept;
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Returns: d_­.
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constexpr operator sys_days() const noexcept;
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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.
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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.
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[Example
: 
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
]
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constexpr explicit operator local_days() const noexcept;
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Returns: local_­days{sys_­days{*this}.time_­since_­epoch()}.
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constexpr bool ok() const noexcept;
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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.