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

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< cpp‎ | chrono‎ | year month weekday

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

Run this code

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

    int main()
    {
        auto ymwi{1/std::chrono::Wednesday[2]/2021};
        std::cout << ymwi << '\n';

        ymwi += std::chrono::years(5);
        std::cout << ymwi << '\n';
        assert(static_cast<std::chrono::year_month_day>(ymwi) ==
                           std::chrono::year(2026)/1/14);

        ymwi -= std::chrono::months(1);
        std::cout << ymwi << '\n';
        assert(static_cast<std::chrono::year_month_day>(ymwi) ==
                           std::chrono::day(10)/12/2025);
    }

Output:

    2021/Jan/Wed[2]
    2026/Jan/Wed[2]
    2025/Dec/Wed[2]

### See also

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

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