std::chrono::year_month::operator+=,std::chrono::year_month::operator-=(3)

NAME
std::chrono::year_month::operator+=,std::chrono::year_month::operator-= - std::chrono::year_month::operator+=,std::chrono::year_month::operator-=

Synopsis
   constexpr std::chrono::year_month& (1) (since C++20)
   operator+=( const std::chrono::years& dy ) const noexcept;
   constexpr std::chrono::year_month& (2) (since C++20)
   operator+=( const std::chrono::months& dm ) const noexcept;
   constexpr std::chrono::year_month& (3) (since C++20)
   operator-=( const std::chrono::years& dy ) const noexcept;
   constexpr std::chrono::year_month& (4) (since C++20)
   operator-=( const std::chrono::months& dm ) const noexcept;
   Modifies the time point *this represents by the duration dy or dm.
   1) Equivalent to *this = *this + dy;
   2) Equivalent to *this = *this + dm;
   3) Equivalent to *this = *this - dy;
   4) Equivalent to *this = *this - dm;
   For durations that are convertible to both std::chrono::years and
   std::chrono::months, the years overloads (1,3) are preferred if the call would
   otherwise be ambiguous.

Example
// Run this code
 #include <iostream>
 #include <chrono>
 int main()
 {
     std::cout << std::boolalpha;
     auto ym {std::chrono::day(1)/7/2023};
     ym -= std::chrono::years {2};
     std::cout << (ym.month() == std::chrono::July) << ' '
               << (ym.year() == std::chrono::year(2021)) << ' ';
     ym += std::chrono::months {7};
     std::cout << (ym.month() == std::chrono::month(2)) << ' '
               << (ym.year() == std::chrono::year(2022)) << '\n';
 }

Output:
 true true true true

See also
   operator+ performs arithmetic on year_month
   operator- (function)
   (C++20)