std::chrono::operator+, std::chrono::operator- (std::chrono::year)

来自cppreference.com
< cpp‎ | chrono‎ | year
 
 
 
 
定义于头文件 <chrono>
constexpr std::chrono::year operator+(const std::chrono::year& y,
                                      const std::chrono::years& ys) noexcept;
(1) (C++20 起)
constexpr std::chrono::year operator+(const std::chrono::years& ys,
                                      const std::chrono::year& y) noexcept;
(2) (C++20 起)
constexpr std::chrono::year operator-(const std::chrono::year& y,
                                      const std::chrono::years& ys) noexcept;
(3) (C++20 起)
constexpr std::chrono::years operator-(const std::chrono::year& y1,
                                       const std::chrono::year& y2) noexcept;
(4) (C++20 起)
1-2)yys.count() 年。
3)y 减去 ys.count() 年。
4) 返回 y1y2 间按年计算的差。

返回值

1-2) std::chrono::year(int(y) + ys.count())
3) std::chrono::year(int(y) - ys.count())
4) std::chrono::years(int(y1) - int(y2))

注解

(1-3) 产生的年份值在范围 [-32767,32767] 外,则实际存储值未指定。

二个 year 值相减的结果是 std::chrono::years 类型时长。此时长单位表示格里高利年的平均长度,而结果与运算数所表示的具体年中的日数无关。例如 2018y - 2017y 的结果是 std::chrono::years(1) ,它表示 365.2425 日,而非 365 日。

示例

#include <iostream>
#include <chrono>
 
int main()
{
 
    std::chrono::year y {2020};
 
    y = y + std::chrono::years(12);
    if (y == std::chrono::year(2032)) {
        std::cout << "Years added correctly" << "\n";
    } else {
        std::cout << "Years not added correctly" << "\n";
    }
 
    y = y - std::chrono::years(33);
    if (y == std::chrono::year(1999)) {
        std::cout << "Years subtracted correctly" << "\n";
    } else {
        std::cout << "Years not subtracted correctly" << "\n";
    }
 
    std::chrono::years ys = std::chrono::year(2025) - std::chrono::year(2020);
    if (ys == std::chrono::years(5)) {
        std::cout << "Years subtracted correctly" << "\n";
    } else {
        std::cout << "Years not subtracted correctly" << "\n";
    }
 
}

输出:

Years added correctly
Years subtracted correctly
Years subtracted correctly

返回值

自增或自减 month
(std::chrono::month 的公开成员函数)
加或减月数
(std::chrono::month 的公开成员函数)