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

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< cpp‎ | 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

Run this code

    #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

operator++operator++(int)operator--operator--(int) | increments or decrements the day (public member function)
operator+=operator-= | adds or subtracts a number of days (public member function)

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