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

< cpp‎ | chrono‎ | year month weekday

constexpr std::chrono::year_month_weekday& operator+=(const std::chrono::years& dy) const noexcept; | (1) | (C++20 起)
constexpr std::chrono::year_month_weekday& operator+=(const std::chrono::months& dm) const noexcept; | (2) | (C++20 起)
constexpr std::chrono::year_month_weekday& operator-=(const std::chrono::years& dy) const noexcept; | (3) | (C++20 起)
constexpr std::chrono::year_month_weekday& operator-=(const std::chrono::months& dm) const noexcept; | (4) | (C++20 起)

以时长 `dy` 或 `dm` 为程度修改时间点 `*this` 。

1) 等价于 *this = *this + dy;
2) 等价于 *this = *this + dm;
3) 等价于 *this = *this - dy;
4) 等价于 *this = *this - dm;

对于能转换到 std::chrono::years 与 std::chrono::months 两者的时长，若调用有歧义，则偏好 `years` 重载 (1,3) 。

### 参阅

operator+operator- (C++20) | 将 `year_month_weekday` 与一定数量的 `years` 或 `months` 相加或相减 (函数)