27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.9 Class month_­day [time.cal.md] 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.