Defined in header <chrono>
constexpr std::chrono::day operator ""d( unsigned long long d ) noexcept;
(since C++20)

Forms a std::chrono::day literal representing a day of the month in the calendar.


d - the day value

Return value

A std::chrono::day storing d. If d > 255, the stored value is unspecified.

Possible implementation

constexpr std::chrono::day operator ""d(unsigned long long d) noexcept
    return std::chrono::day(d);


This operator is declared in the namespace std::literals::chrono_literals, where both literals and chrono_literals are inline namespaces. Access to this operator can be gained with:

  • using namespace std::literals,
  • using namespace std::chrono_literals, or
  • using namespace std::literals::chrono_literals.

In addition, within the namespace std::chrono, the directive using namespace literals::chrono_literals; is provided by the standard library, so that if a programmer uses using namespace std::chrono; to gain access to the classes in the chrono library, the corresponding literal operators become visible as well.


#include <chrono>
#include <iostream>
int main()
    using namespace std::literals::chrono_literals;
    std::cout << static_cast<unsigned>(42d) << ' '
              << static_cast<unsigned>(256d) << ' ' // unspecified
              << static_cast<unsigned>(298d) << '\n'; // unspecified

Possible output:

42 0 42

See also

constructs a day
(public member function of std::chrono::day)
retrieves the stored day value
(public member function of std::chrono::day)

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