29 Time library [time]

29.8 The civil calendar [time.cal]

29.8.13 Class year_month [time.cal.ym]

29.8.13.2 Member functions [time.cal.ym.members]

constexpr year_month(const chrono::year& y, const chrono::month& m) noexcept;
Effects: Initializes y_ with y, and m_ with m.
constexpr chrono::year year() const noexcept;
Returns: y_.
constexpr chrono::month month() const noexcept;
Returns: m_.
constexpr year_month& operator+=(const months& dm) noexcept;
Constraints: If the argument supplied by the caller for the months parameter is convertible to years, its implicit conversion sequence to years is worse than its implicit conversion sequence to months ([over.ics.rank]).
Effects: *this = *this + dm.
Returns: *this.
constexpr year_month& operator-=(const months& dm) noexcept;
Constraints: If the argument supplied by the caller for the months parameter is convertible to years, its implicit conversion sequence to years is worse than its implicit conversion sequence to months ([over.ics.rank]).
Effects: *this = *this - dm.
Returns: *this.
constexpr year_month& operator+=(const years& dy) noexcept;
Effects: *this = *this + dy.
Returns: *this.
constexpr year_month& operator-=(const years& dy) noexcept;
Effects: *this = *this - dy.
Returns: *this.
constexpr bool ok() const noexcept;
Returns: y_.ok() && m_.ok().