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

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< cpp‎ | chrono‎ | year month day

Defined in header `<chrono>` |  |
constexpr std::chrono::year_month_day operator+( const std::chrono::year_month_day & ymd, const std::chrono::months & dm ) noexcept; |  | (since C++20)
constexpr std::chrono::year_month_day operator+( const std::chrono::months & dm, const std::chrono::year_month_day & ymd ) noexcept; |  | (since C++20)
constexpr std::chrono::year_month_day operator+( const std::chrono::year_month_day & ymd, const std::chrono::years & dy ) noexcept; |  | (since C++20)
constexpr std::chrono::year_month_day operator+( const std::chrono::years & dy, const std::chrono::year_month_day & ymd ) noexcept; |  | (since C++20)
constexpr std::chrono::year_month_day operator-( const std::chrono::year_month_day & ymd, const std::chrono::months & dm ) noexcept; |  | (since C++20)
constexpr std::chrono::year_month_day operator-( const std::chrono::year_month_day & ymd, const std::chrono::years & dy ) noexcept; |  | (since C++20)

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

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