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

 

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std::chrono::weekday

成员函数

weekday::weekday

weekday::operator++weekday::operator--

weekday::operator+=weekday::operator-=

weekday::c_encodingweekday::iso_encoding

weekday::ok

weekday::operator[]

非成员函数

operator==

operator+operator-

operator<<

from_stream

辅助类

formatter<std::chrono::weekday>

 

constexpr std::chrono::weekday operator+(const std::chrono::weekday& wd,                                          const std::chrono::days& d) noexcept;	(1)	(C++20 起)
constexpr std::chrono::weekday operator+(const std::chrono::days& d,                                          const std::chrono::weekday& wd) noexcept;	(2)	(C++20 起)
constexpr std::chrono::weekday operator-(const std::chrono::weekday& wd,                                          const std::chrono::days& d) noexcept;	(3)	(C++20 起)
constexpr std::chrono::days operator-(const std::chrono::weekday& wd1,                                       const std::chrono::weekday& wd2) noexcept;	(4)	(C++20 起)

1-2) 向 wd 加上 d.count() 日。通过首先求值 static_cast<long long>(wd.c_encoding()) + d.count() 再将它对 7 取余，得到范围 [0, 6] 中的整数，计算结果中保有的星期之日值。

3) 从 wd 减去 d.count() 日。等价于 return wd + -d; 。

4) 若 wd1.ok() 与 wd2.ok() 均为 true ，则返回 std::chrono::days 值 d ，满足 d.count() 在范围 [0, 6] 中且 wd2 + d == wd1 。否则返回值未指定。

返回值

1-3) 保有按上述方式计算的星期之日值的 std::chrono::weekday 。

4) 表示 wd1 与 wd2 间距离的 std::chrono::days 。

注意

只要计算不溢出， (1-3) 就始终返回合法的 weekday ，即使 wd.ok() 为 false 。

示例

运行此代码

#include <iostream>
#include <chrono>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::chrono::weekday wd {4};
    wd = wd + std::chrono::days(2);
    std::cout << (wd == std::chrono::weekday(6)) << ' '
              << (wd == std::chrono::Saturday) << ' ';
 
    wd = wd - std::chrono::days(3);
    std::cout << (wd == std::chrono::weekday(3)) << ' '
              << (wd == std::chrono::Wednesday) << ' ';
 
    wd = std::chrono::Tuesday;
    wd = wd + std::chrono::days{8}; // (((2 + 8) == 10) % 7) == 3;
    std::cout << (wd == std::chrono::Wednesday) << ' ';
 
    wd = wd + (std::chrono::Sunday - std::chrono::Thursday); // (3 + 3) == 6
    std::cout << (wd == std::chrono::Saturday) << '\n';
}

输出：

true true true true true true

参阅

operator++operator++(int)operator--operator--(int)	自增或自减 weekday (公开成员函数)
operator+=operator-=	加或减日数 (公开成员函数)