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

 

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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::days& d) noexcept;	(1)	(C++20 起)
constexpr std::chrono::weekday& operator-=(const std::chrono::days& d) noexcept;	(2)	(C++20 起)

对星期之日值加或减 d.count() ，将结果对 7 取余，规约成范围 [0, 6] 中的整数。

1) 进行 *this = *this + d;

2) 进行 *this = *this - d;

返回值

到修改后的此 weekday 的引用。

注意

调用这些函数之一后，若运算中不出现溢出，则 ok() 始终为 true 。

示例

运行此代码

#include <iostream>
#include <chrono>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::chrono::weekday wd {5}; // Friday is 5
    wd += std::chrono::days(2);
    std::cout << (wd == std::chrono::weekday(0)) << ' '
              << (wd == std::chrono::Sunday) << ' ';
 
    wd -= std::chrono::days(3);
    std::cout << (wd == std::chrono::weekday(4)) << ' '
              << (wd == std::chrono::Thursday) << ' ';
 
    wd = std::chrono::Wednesday;
    wd += std::chrono::days{8}; // ((3 += 8 == 11) % 7) == 4;
    std::cout << (wd == std::chrono::Thursday) << ' ';
 
    wd -= (std::chrono::Sunday - std::chrono::Tuesday); // -= -2
    // (4 -= -2) == 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- (C++20)	在 weekday 上进行算术 (函数)