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

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< cpp‎ | chrono‎ | year month weekday

constexpr std::chrono::year_month_weekday operator+( const std::chrono::year_month_weekday & ymwd, const std::chrono::months & dm ) noexcept; | (1) | (since C++20)
constexpr std::chrono::year_month_weekday operator+( const std::chrono::months & dm, const std::chrono::year_month_weekday & ymwd ) noexcept; | (2) | (since C++20)
constexpr std::chrono::year_month_weekday operator+( const std::chrono::year_month_weekday & ymwd, const std::chrono::years & dy ) noexcept; | (3) | (since C++20)
constexpr std::chrono::year_month_weekday operator+( const std::chrono::years & dy, const std::chrono::year_month_weekday & ymwd ) noexcept; | (4) | (since C++20)
constexpr std::chrono::year_month_weekday operator-( const std::chrono::year_month_weekday & ymwd, const std::chrono::months & dm ) noexcept; | (5) | (since C++20)
constexpr std::chrono::year_month_weekday operator-( const std::chrono::year_month_weekday & ymwd, const std::chrono::years & dy ) noexcept; | (6) | (since C++20)

1,2) Adds dm.count() months to the date represented by ymwd. The result has the same `year()` and `month()` as std::chrono::year_month (ymwd.year(), ymwd.month()) + dm and the same `weekday()` and `index()` as ymwd.
3,4) Adds dy.count() years to the date represented by ymwd. The result is equivalent to std::chrono::year_month_weekday (ymwd.year() + dy, ymwd.month(), ymwd.weekday_indexed()).
5) Subtracts dm.count() months from the date represented by ymwd. Equivalent to ymwd + -dm.
6) Subtracts dy.count() years from the date represented by ymwd. Equivalent to ymwd + -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 ymwd.ok() is true, the resulting `year_month_weekday` may not represent a valid date if ymwd.index() is 5.

### Example

Run this code

    #include <cassert>
    #include <chrono>
    #include <iostream>

    int main()
    {
        auto ymwdi{1/std::chrono::Wednesday[1]/2021};
        std::cout << ymwdi << '\n';

        ymwdi = std::chrono::years(5) + ymwdi;
        // First Wednesday in January, 2026
        std::cout << ymwdi << '\n';
        assert(static_cast<std::chrono::year_month_day>(ymwdi) ==
               std::chrono::January/7/2026);

        ymwdi = ymwdi - std::chrono::months(6);
        // First Wednesday in July, 2025
        std::cout << ymwdi << '\n';
        assert(static_cast<std::chrono::year_month_day>(ymwdi) ==
               std::chrono::July/2/2025);
    }

Output:

    2021/Jan/Wed[1]
    2026/Jan/Wed[1]
    2025/Jul/Wed[1]

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