NAME¶

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

Synopsis¶

constexpr std::chrono::weekday& operator+=( const (1) (since C++20)
std::chrono::days& d ) noexcept;
constexpr std::chrono::weekday& operator-=( const (2) (since C++20)
std::chrono::days& d ) noexcept;

Adds or subtracts d.count() from the weekday value, reducing the result modulo 7 to
an integer in the range [0, 6].

1) Performs *this = *this + d;.
2) Performs *this = *this - d;.

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¶

// Run this code

#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';
}

Output:¶

true true true true true true

See also¶

operator++
operator++(int) increments or decrements the weekday
operator-- (public member function)
operator--(int)
operator+ performs arithmetic on weekdays
operator- (function)
(C++20)