30 Time library [time]

30.8 The civil calendar [time.cal]

30.8.4 Class month [time.cal.month]

30.8.4.3 Non-member functions [time.cal.month.nonmembers]

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

Returns: unsigned{x} == unsigned{y}.

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constexpr strong_ordering operator<=>(const month& x, const month& y) noexcept;

Returns: unsigned{x} <=> unsigned{y}.

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constexpr month operator+(const month& x, const months& y) noexcept;

Returns: month{modulo(static_cast<long long>(unsigned{x}) + (y.count() - 1), 12) + 1} where modulo(n, 12) computes the remainder of n divided by 12 using Euclidean division.

[Note 1:

Given a divisor of 12, Euclidean division truncates towards negative infinity and always produces a remainder in the range of [0, 11].

Assuming no overflow in the signed summation, this operation results in a month holding a value in the range [1, 12] even if !x.ok().

— end note]

[Example 1:

February + months{11} == January.

— end example]

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constexpr month operator+(const months& x, const month& y) noexcept;

Returns: y + x.

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constexpr month operator-(const month& x, const months& y) noexcept;

Returns: x + -y.

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constexpr months operator-(const month& x, const month& y) noexcept;

Returns: If x.ok() == true and y.ok() == true, returns a value m in the range [months{0}, months{11}] satisfying y + m == x.

Otherwise the value returned is unspecified.

[Example 2:

January - February == months{11}.

— end example]

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template<class charT, class traits>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const month& m);

Effects: Equivalent to: return os << (m.ok() ? format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%b}"), m) : format(os.getloc(), STATICALLY-WIDEN<charT>("{} is not a valid month"), static_cast<unsigned>(m)));

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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,
                month& m, basic_string<charT, traits, Alloc>* abbrev = nullptr,
                minutes* offset = nullptr);

Effects: Attempts to parse the input stream is into the month m using the format flags given in the NTCTS fmt as specified in [time.parse].

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