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

< cpp‎ | chrono‎ | weekday
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Defined in header <chrono>
constexpr std::chrono::weekday operator+( const std::chrono::weekday& wd,
                                          const std::chrono::days& d ) noexcept;
(1) (since C++20)
constexpr std::chrono::weekday operator+( const std::chrono::days& d,
                                          const std::chrono::weekday& wd ) noexcept;
(2) (since C++20)
constexpr std::chrono::weekday operator-( const std::chrono::weekday& wd,
                                          const std::chrono::days& d ) noexcept;
(3) (since C++20)
constexpr std::chrono::days operator-( const std::chrono::weekday& wd1,
                                       const std::chrono::weekday& wd2 ) noexcept;
(4) (since C++20)
1,2) Adds d.count() days to wd. The weekday value held in the result is computed by first evaluating static_cast<long long>(wd.c_encoding()) + d.count() and reducing it modulo 7 to an integer in the range [06].
3) Subtracts d.count() days from wd. Equivalent to return wd + -d;.
4) If wd1.ok() and wd2.ok() are both true, returns a std::chrono::days value d such that d.count() is in the range [06] and wd2 + d == wd1. Otherwise the returned value is unspecified.


[edit] Return value

1-3) A std::chrono::weekday holding a weekday value calculated as described above.
4) A std::chrono::days representing the distance between wd1 and wd2.

[edit] Notes

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

[edit] 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';


true true true true true true

[edit] See also

increments or decrements the weekday
(public member function) [edit]
adds or subtracts a number of days
(public member function) [edit]