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

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Utilities library
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chrono I/O
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C-style date and time
std::chrono::year_month
constexpr std:: chrono :: year_month &
operator + = ( const std:: chrono :: years & dy ) const noexcept ;
(1) (since C++20)
constexpr std:: chrono :: year_month &
operator + = ( const std:: chrono :: months & dm ) const noexcept ;
(2) (since C++20)
constexpr std:: chrono :: year_month &
operator - = ( const std:: chrono :: years & dy ) const noexcept ;
(3) (since C++20)
constexpr std:: chrono :: year_month &
operator - = ( const std:: chrono :: months & dm ) const noexcept ;
(4) (since C++20)

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

(C++20)
performs arithmetic on year_month
(function)
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