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

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.

# Declarations

constexpr std::chrono::year_month_weekday
operator+( const std::chrono::year_month_weekday& ymwd,
const std::chrono::months& dm ) noexcept;

(since C++20)

constexpr std::chrono::year_month_weekday
operator+( const std::chrono::months& dm,
const std::chrono::year_month_weekday& ymwd ) noexcept;

(since C++20)

constexpr std::chrono::year_month_weekday
operator+( const std::chrono::year_month_weekday& ymwd,
const std::chrono::years& dy ) noexcept;

(since C++20)

constexpr std::chrono::year_month_weekday
operator+( const std::chrono::years& dy,
const std::chrono::year_month_weekday& ymwd ) noexcept;

(since C++20)

constexpr std::chrono::year_month_weekday
operator-( const std::chrono::year_month_weekday& ymwd,
const std::chrono::months& dm ) noexcept;

(since C++20)

constexpr std::chrono::year_month_weekday
operator-( const std::chrono::year_month_weekday& ymwd,
const std::chrono::years& dy ) noexcept;

(since C++20)

# Notes

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

# Example

#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);
}