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

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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.

[edit] Example

#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));
}

[edit] See also

adds or subtracts a year_month_day_last and some number of years or months
(function) [edit]