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

From cppreference.com
< cpp‎ | chrono‎ | weekday
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
 
 
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 [0, 6].
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 [0, 6] and wd2 + d == wd1. Otherwise the returned value is unspecified.

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.

Notes

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

Example

#include <iostream>
#include <chrono>
 
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';
}

Output:

true true true true true true

See also

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