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

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< cpp‎ | chrono‎ | weekday
 
C++
 
日期和时间库
时间点
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(C++20)  
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时长
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时钟
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(C++20)
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当天时刻
(C++20)(C++20)
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日历
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chrono I/O
(C++20)

 
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���成范围 [​0​, 6] 中的整数。

1) 实施 *this = *this + d;。
2) 实施 *this = *this - d;。

目录

[编辑] 返回值

到修改后的此 weekday 的引用。

[编辑] 注解

调用这些函数之一后，若运算中不出现溢出，则 ok() 始终为 true。

[编辑] 示例

运行此代码
#include <chrono>
#include <iostream>
 
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

[编辑] 参阅

 自增或自减 weekday
(公开成员函数) [编辑]
(C++20)
 在 weekday 上进行算术
(函数) [编辑]
来自“https://zh.cppreference.com/mwiki/index.php?title=cpp/chrono/weekday/operator_arith&oldid=81935”