27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.9 Class month_­day [time.cal.md]

27.8.9.1 Overview [time.cal.md.overview]

namespace std::chrono {
  class month_day {
    chrono::month m_;           // exposition only
    chrono::day   d_;           // exposition only

  public:
    month_day() = default;
    constexpr month_day(const chrono::month& m, const chrono::day& d) noexcept;

    constexpr chrono::month month() const noexcept;
    constexpr chrono::day   day()   const noexcept;
    constexpr bool ok() const noexcept;
  };
}
month_­day represents a specific day of a specific month, but with an unspecified year.
month_­day meets the Cpp17EqualityComparable (Table 23) and Cpp17LessThanComparable (Table 24) requirements.
month_­day is a trivially copyable and standard-layout class type.

27.8.9.2 Member functions [time.cal.md.members]

constexpr month_day(const chrono::month& m, const chrono::day& d) noexcept;
Effects: Initializes m_­ with m, and d_­ with d.
constexpr chrono::month month() const noexcept;
Returns: m_­.
constexpr chrono::day day() const noexcept;
Returns: d_­.
constexpr bool ok() const noexcept;
Returns: true if m_­.ok() is true, 1d <= d_­, and d_­ is less than or equal to the number of days in month m_­; otherwise returns false.
When m_­ == February, the number of days is considered to be 29.

27.8.9.3 Non-member functions [time.cal.md.nonmembers]

constexpr bool operator==(const month_day& x, const month_day& y) noexcept;
Returns: x.month() == y.month() && x.day() == y.day().
constexpr strong_ordering operator<=>(const month_day& x, const month_day& y) noexcept;
Effects: Equivalent to:
if (auto c = x.month() <=> y.month(); c != 0) return c;
return x.day() <=> y.day();
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const month_day& md);
Effects: Equivalent to:
return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{}"),
                    md.month(), md.day());
template<class charT, class traits, class Alloc = allocator<charT>> basic_istream<charT, traits>& from_stream(basic_istream<charT, traits>& is, const charT* fmt, month_day& md, basic_string<charT, traits, Alloc>* abbrev = nullptr, minutes* offset = nullptr);
Effects: Attempts to parse the input stream is into the month_­day md using the format flags given in the NTCTS fmt as specified in [time.parse].
If the parse fails to decode a valid month_­day, is.setstate(ios_­base​::​failbit) is called and md 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.