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

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].

# Declarations

constexpr std::chrono::weekday& operator+=( const std::chrono::days& d ) noexcept;

(since C++20)

constexpr std::chrono::weekday& operator-=( const std::chrono::days& d ) noexcept;

(since C++20)

# 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

#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';
}

# See also