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

From cppreference.net
C++
Date and time library
std::chrono::weekday
constexpr std:: chrono :: weekday & operator + = ( const std:: chrono :: days & d ) noexcept ;
(1) (自 C++20 起)
constexpr std:: chrono :: weekday & operator - = ( const std:: chrono :: days & d ) noexcept ;
(2) (自 C++20 起)

将工作日数值增加或减少 d. count ( ) ，并将结果对7取模，最终得到范围在 [ ​ 0 ​ , 6 ] 之间的整数值。

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

目录

返回值

对此 weekday 修改后的引用。

注释

在调用这些函数之一后，若操作期间未发生溢出， ok() 将始终返回 true。

示例

运行此代码 
#include <chrono>
#include <iostream>
int main()
{
    std::cout << std::boolalpha;
    std::chrono::weekday wd{5}; // 星期五对应数值 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

参见

递增或递减 weekday 对象
(公开成员函数)
(C++20)
对 weekday 对象执行算术运算
(函数)