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>

formatter<std::chrono::hash> (C++26)

 

在标头 <chrono> 定义
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，以此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。

注解

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 <chrono>
#include <iostream>
 
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-=	加上或减去天数 (公开成员函数)