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

Since C++20

Header: <chrono>

1,2) Adds d.count() days to wd. The weekday value held in the result is computed by first evaluating static_cast(wd.c_encoding()) + d.count() and reducing it modulo 7 to an integer in the range [0,6].

# Declarations

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

(since C++20)

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

(since C++20)

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

(since C++20)

constexpr std::chrono::days operator-( const std::chrono::weekday& wd1,
const std::chrono::weekday& wd2 ) noexcept;

(since C++20)

# Notes

As long as the computation doesn’t overflow, (1-3) always return a valid weekday even if wd.ok() is false.

# Example

#include <chrono>
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::chrono::weekday wd{4};
    wd = wd + std::chrono::days(2);
    std::cout << (wd == std::chrono::weekday(6)) << ' '
              << (wd == std::chrono::Saturday) << ' ';
 
    wd = wd - std::chrono::days(3);
    std::cout << (wd == std::chrono::weekday(3)) << ' '
              << (wd == std::chrono::Wednesday) << ' ';
 
    wd = std::chrono::Tuesday;
    wd = wd + std::chrono::days{8}; // (((2 + 8) == 10) % 7) == 3;
    std::cout << (wd == std::chrono::Wednesday) << ' ';
 
    wd = wd + (std::chrono::Sunday - std::chrono::Thursday); // (3 + 3) == 6
    std::cout << (wd == std::chrono::Saturday) << '\n';
}

# See also