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

Defined in header <chrono> 
constexpr std::chrono::day operator+( const std::chrono::day&  d,
                                      const std::chrono::days& ds ) noexcept;
 (1) (since C++20) 
constexpr std::chrono::day operator+( const std::chrono::days& ds,
                                      const std::chrono::day&  d ) noexcept;
 (2) (since C++20) 
constexpr std::chrono::day operator-( const std::chrono::day&  d,
                                      const std::chrono::days& ds ) noexcept;
 (3) (since C++20) 
constexpr std::chrono::days operator-( const std::chrono::day& x,
                                       const std::chrono::day& y ) noexcept;
 (4) (since C++20)
1-2) Adds ds.count() days to d.
3) Subtracts ds.count() days from d.
4) Calculate the difference, in days, between two day x and y.

Return value

1-2) std::chrono::day(unsigned(d) + ds.count())
3) std::chrono::day(unsigned(d) - ds.count())
4) std::chrono::days(int(unsigned(x)) - int(unsigned(y)))

Notes

For (1-3), if the result would be outside the range [0, 255], the actual stored value is unspecified.

Example

#include <chrono>
#include <cassert>
 
int main()
{
    std::chrono::day d {15};
 
    d = d + std::chrono::days(2);
    assert(d == std::chrono::day(17));
 
    d = d - std::chrono::days(3);
    assert(d == std::chrono::day(14));
 
    constexpr std::chrono::days ds = std::chrono::day(16) - std::chrono::day(14);
    static_assert(ds == std::chrono::days(2));
}

See also

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

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