std::chrono:: operator+, std::chrono:: operator- (std::chrono::year_month_weekday)

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chrono I/O
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C-style date and time
std::chrono::year_month_weekday
(1) (since C++20)
(2) (since C++20)
(3) (since C++20)
(4) (since C++20)
(5) (since C++20)
(6) (since C++20)
1,2) Adds dm. count ( ) months to the date represented by ymwd . The result has the same year() and month() as std:: chrono :: year_month ( ymwd. year ( ) , ymwd. month ( ) ) + dm and the same weekday() and index() as ymwd .
3,4) Adds dy. count ( ) years to the date represented by ymwd . The result is equivalent to std:: chrono :: year_month_weekday ( ymwd. year ( ) + dy, ymwd. month ( ) , ymwd. weekday_indexed ( ) ) .
5) Subtracts dm. count ( ) months from the date represented by ymwd . Equivalent to ymwd + - dm .
6) Subtracts dy. count ( ) years from the date represented by ymwd . Equivalent to ymwd + - dy .

For durations that are convertible to both std::chrono::years and std::chrono::months , the years overloads (3,4,6) are preferred if the call would otherwise be ambiguous.

Notes

Even if ymwd. ok ( ) is true , the resulting year_month_weekday may not represent a valid date if ymwd. index ( ) is 5 .

Example

Run this code 
#include <cassert>
#include <chrono>
#include <iostream>
 
int main()
{
    auto ymwdi{1/std::chrono::Wednesday[1]/2021};
    std::cout << ymwdi << '\n';
 
    ymwdi = std::chrono::years(5) + ymwdi;
    // First Wednesday in January, 2026
    std::cout << ymwdi << '\n';
    assert(static_cast<std::chrono::year_month_day>(ymwdi) ==
           std::chrono::January/7/2026);
 
    ymwdi = ymwdi - std::chrono::months(6);
    // First Wednesday in July, 2025
    std::cout << ymwdi << '\n';
    assert(static_cast<std::chrono::year_month_day>(ymwdi) ==
           std::chrono::July/2/2025);
}

Output: 

2021/Jan/Wed[1]
2026/Jan/Wed[1]
2025/Jul/Wed[1]
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