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

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Date and time utilities
Time point
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Duration
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Time of day
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Calendar
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chrono I/O
(C++20)
C-style date and time
std::chrono::weekday
constexpr std:: chrono :: weekday & operator + = ( const std:: chrono :: days & d ) noexcept ;
(1) (since C++20)
constexpr std:: chrono :: weekday & operator - = ( const std:: chrono :: days & d ) noexcept ;
(2) (since C++20)

Adds or subtracts d. count ( ) from the weekday value, reducing the result modulo 7 to an integer in the range [ ​ 0 ​ , 6 ] .

1) Performs * this = * this + d ; .
2) Performs * this = * this - d ; .

Return value

A reference to this weekday after modification.

Notes

After a call to one of these functions, ok() is always true if no overflow occurred during the operation.

Example

Run this code 
#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';
}

Output: 

true true true true true true

See also

increments or decrements the weekday
(public member function)
(C++20)
performs arithmetic on weekday s
(function)
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