27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.6 Class weekday [time.cal.wd]

27.8.6.3 Non-member functions [time.cal.wd.nonmembers]

constexpr bool operator==(const weekday& x, const weekday& y) noexcept;

Returns: x.wd_ == y.wd_.

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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]

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constexpr weekday operator+(const days& x, const weekday& y) noexcept;

Returns: y + x.

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constexpr weekday operator-(const weekday& x, const days& y) noexcept;

Returns: x + -y.

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constexpr days operator-(const weekday& x, const weekday& y) noexcept;

Returns: If x.ok() == true and y.ok() == true, returns a value d in the range [days{0}, days{6}] satisfying y + d == x.

Otherwise the value returned is unspecified.

[Example 2:

Sunday - Monday == days{6}.

— end example]

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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>("{:%a}"), wd) : format(os.getloc(), STATICALLY-WIDEN<charT>("{} is not a valid weekday"), static_cast<unsigned>(wd.wd_)));

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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 is into the weekday wd using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid weekday, is.setstate(ios_base::failbit) is called and wd 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.

Returns: is.