std::chrono::operator+,std::chrono::operator-(std::chrono::year_month_day)(3)

NAME
std::chrono::operator+,std::chrono::operator-(std::chrono::year_month_day) - std::chrono::operator+,std::chrono::operator-(std::chrono::year_month_day)

Synopsis
   Defined in header <chrono>
   constexpr std::chrono::year_month_day operator+( const
   std::chrono::year_month_day& ymd,
                        const (since C++20)
   std::chrono::months& dm
                        ) noexcept;
   constexpr std::chrono::year_month_day operator+( const
   std::chrono::months& dm,
                        const (since C++20)
   std::chrono::year_month_day& ymd
                        ) noexcept;
   constexpr std::chrono::year_month_day operator+( const
   std::chrono::year_month_day& ymd,
                        const (since C++20)
   std::chrono::years& dy
                        ) noexcept;
   constexpr std::chrono::year_month_day operator+( const
   std::chrono::years& dy,
                        const (since C++20)
   std::chrono::year_month_day& ymd
                        ) noexcept;
   constexpr std::chrono::year_month_day operator-( const
   std::chrono::year_month_day& ymd,
                        const (since C++20)
   std::chrono::months& dm
                        ) noexcept;
   constexpr std::chrono::year_month_day operator-( const
   std::chrono::year_month_day& ymd,
                        const (since C++20)
   std::chrono::years& dy
                        ) noexcept;
   1,2) Adds dm.count() months to the date represented by ymd. The result has the same
   day() as ymd and the same year() and month() as std::chrono::year_month(ymd.year(),
   ymd.month()) + dm.
   3,4) Adds dy.count() years to the date represented by ymd. The result is equivalent
   to std::chrono::year_month_day(ymd.year() + dy, ymd.month(), ymd.day().
   5) Subtracts dm.count() months from the date represented by ymd. Equivalent to ymd +
   -dm.
   6) Subtracts dy.count() years from the date represented by ymd. Equivalent to ymd +
   -dy.
   For durations that are convertible to both std::chrono::years and
   std::chrono::months, the years overloads (3,4,6) are preferred if the call would
   otherwise be ambiguous.

Notes
   Even if ymd.ok() is true, the resulting year_month_day may not represent a valid
   date if ymd.day() is 29, 30, or 31.

Example
// Run this code
 #include <chrono>
 #include <iostream>
 int main()
 {
     std::cout << std::boolalpha;
     auto ymd{std::chrono::day(1)/std::chrono::July/2021};
     ymd = ymd + std::chrono::months(4);
     std::cout << (ymd.month() == std::chrono::November) << ' '
               << (ymd.year() == std::chrono::year(2021)) << ' ';
     ymd = ymd - std::chrono::years(10);
     std::cout << (ymd.month() == std::chrono::month(11)) << ' '
               << (ymd.year() == std::chrono::year(2011)) << '\n';
 }

Output:
 true true true true