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

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< cpp‎ | chrono‎ | year month day last

constexpr std::chrono::year_month_day_last & operator+=( const std::chrono::years & dy ) const noexcept; | (1) | (since C++20)
constexpr std::chrono::year_month_day_last & operator+=( const std::chrono::months & dm ) const noexcept; | (2) | (since C++20)
constexpr std::chrono::year_month_day_last & operator-=( const std::chrono::years & dy ) const noexcept; | (3) | (since C++20)
constexpr std::chrono::year_month_day_last & 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 ymdl{11/std::chrono::last/2020};

        ymdl += std::chrono::years(15);
        assert(ymdl.day() == std::chrono::day(30));
        assert(ymdl.month() == std::chrono::November);
        assert(ymdl.year() == std::chrono::year(2035));

        ymdl -= std::chrono::months(6);
        assert(ymdl.day() == std::chrono::day(31));
        assert(ymdl.month() == std::chrono::May);
        assert(ymdl.year() == std::chrono::year(2035));
    }

### See also

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

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