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 <cassert>
 #include <chrono>
 int main()
 {
     auto ym{std::chrono::day(1)/7/2023};
     ym -= std::chrono::years{2};
     assert(ym.month() == std::chrono::July);
     assert(ym.year() == std::chrono::year(2021));
     ym += std::chrono::months{7};
     assert(ym.month() == std::chrono::month(2));
     assert(ym.year() == std::chrono::year(2022));
 }

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