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

constexpr std::chrono::year_month_weekday&
          operator+=( const std::chrono::years& dy ) const noexcept;
 (1) (since C++20) 
constexpr std::chrono::year_month_weekday&
          operator+=( const std::chrono::months& dm ) const noexcept;
 (2) (since C++20) 
constexpr std::chrono::year_month_weekday&
          operator-=( const std::chrono::years& dy ) const noexcept;
 (3) (since C++20) 
constexpr std::chrono::year_month_weekday&
          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 

#include <iostream>
#include <chrono>
 
int main()
{
    std::cout << std::boolalpha;
 
    auto ymwi {1/std::chrono::Wednesday[2]/2021};
    ymwi += std::chrono::years(5);
    std::cout << (static_cast<std::chrono::year_month_day>(ymwi) ==
                              std::chrono::year(2026)/1/14) << ' ';
    ymwi -= std::chrono::months(1);
    std::cout << (static_cast<std::chrono::year_month_day>(ymwi) == 
                              std::chrono::day(10)/12/2025) << '\n';
}

Output:

true true

See also

(C++20)
 adds or subtracts a year_month_weekday and some number of years or months
(function)

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