[time.cal.wd] (original) (raw)
30 Time library [time]
30.8 The civil calendar [time.cal]
30.8.6 Class weekday [time.cal.wd]
30.8.6.1 Overview [time.cal.wd.overview]
namespace std::chrono { class weekday { unsigned char wd_; public: weekday() = default;constexpr explicit weekday(unsigned wd) noexcept;constexpr weekday(const sys_days& dp) noexcept;constexpr explicit weekday(const local_days& dp) noexcept;constexpr weekday& operator++() noexcept;constexpr weekday operator++(int) noexcept;constexpr weekday& operator--() noexcept;constexpr weekday operator--(int) noexcept;constexpr weekday& operator+=(const days& d) noexcept;constexpr weekday& operator-=(const days& d) noexcept;constexpr unsigned c_encoding() const noexcept;constexpr unsigned iso_encoding() const noexcept;constexpr bool ok() const noexcept;constexpr weekday_indexed operator[](unsigned index) const noexcept;constexpr weekday_last operator[](last_spec) const noexcept;};}
weekday represents a day of the week in the civil calendar.
It normally holds values in the range 0 to 6, corresponding to Sunday through Saturday, but it may hold non-negative values outside this range.
It can be constructed with any unsigned value, which will be subsequently truncated to fit into weekday's unspecified internal storage.
[Note 1:
weekday is notCpp17LessThanComparablebecause there is no universal consensus on which day is the first day of the week.
weekday's arithmetic operations treat the days of the week as a circular range, with no beginning and no end.
— _end note_]
weekday is a trivially copyable and standard-layout class type.
30.8.6.2 Member functions [time.cal.wd.members]
constexpr explicit weekday(unsigned wd) noexcept;
Effects: Initializes wd_ with wd == 7 ? 0 : wd.
The value held is unspecified if wd is not in the range [0, 255].
constexpr weekday(const sys_days& dp) noexcept;
Effects: Computes what day of the week corresponds to the sys_days dp, and initializes that day of the week in wd_.
[Example 1:
If dp represents 1970-01-01, the constructed weekday represents Thursday by storing 4 in wd_.
— _end example_]
constexpr explicit weekday(const local_days& dp) noexcept;
Effects: Computes what day of the week corresponds to the local_days dp, and initializes that day of the week in wd_.
Postconditions: The value is identical to that constructed fromsys_days{dp.time_since_epoch()}.
constexpr weekday& operator++() noexcept;
Effects: *this += days{1}.
constexpr weekday operator++(int) noexcept;
Returns: A copy of *this as it existed on entry to this member function.
constexpr weekday& operator--() noexcept;
Effects: *this -= days{1}.
constexpr weekday operator--(int) noexcept;
Returns: A copy of *this as it existed on entry to this member function.
constexpr weekday& operator+=(const days& d) noexcept;
Effects: *this = *this + d.
constexpr weekday& operator-=(const days& d) noexcept;
Effects: *this = *this - d.
constexpr unsigned c_encoding() const noexcept;
constexpr unsigned iso_encoding() const noexcept;
Returns: wd_ == 0u ? 7u : wd_.
constexpr bool ok() const noexcept;
constexpr weekday_indexed operator[](unsigned index) const noexcept;
constexpr weekday_last operator[](last_spec) const noexcept;
Returns: weekday_last{*this}.
30.8.6.3 Non-member functions [time.cal.wd.nonmembers]
constexpr bool operator==(const weekday& x, const weekday& y) noexcept;
constexpr weekday operator+(const weekday& x, const days& y) noexcept;
Returns: weekday{modulo(static_cast<long long>(x.wd_) + y.count(), 7)} where modulo(n, 7) computes the remainder of n divided by 7 using Euclidean division.
[Note 1:
Given a divisor of 7, Euclidean division truncates towards negative infinity and always produces a remainder in the range of [0, 6].
Assuming no overflow in the signed summation, this operation results in a weekday holding a value in the range [0, 6] even if !x.ok().
— _end note_]
[Example 1:
Monday + days{6} == Sunday.
— _end example_]
constexpr weekday operator+(const days& x, const weekday& y) noexcept;
constexpr weekday operator-(const weekday& x, const days& y) noexcept;
constexpr days operator-(const weekday& x, const weekday& y) noexcept;
Returns: If x.ok() == trueand y.ok() == true, returns a value din the range [days{0}, days{6}] satisfying y + d == x.
Otherwise the value returned is unspecified.
[Example 2:
Sunday - Monday == days{6}.
— _end example_]
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const weekday& wd);
Effects: Equivalent to:return os << (wd.ok() ? format(os.getloc(), _STATICALLY-WIDEN_<charT>("{:L%a}"), wd) : format(os.getloc(), STATICALLY-WIDEN<charT>("{} is not a valid weekday"),static_cast<unsigned>(wd.wd_)));
template<class charT, class traits, class Alloc = allocator<charT>> basic_istream<charT, traits>& from_stream(basic_istream<charT, traits>& is, const charT* fmt, weekday& wd, basic_string<charT, traits, Alloc>* abbrev = nullptr, minutes* offset = nullptr);
Effects: Attempts to parse the input stream isinto the weekday wd using the format flags given in the NTCTS fmtas specified in [time.parse].
If the parse fails to decode a valid weekday,is.setstate(ios_base::failbit) is called andwd is not modified.
If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.
If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.