std::literals::chrono_literals::operator""d(3)

NAME
std::literals::chrono_literals::operator""d - std::literals::chrono_literals::operator""d

Synopsis
   Defined in header <chrono>
   constexpr std::chrono::day operator ""d( unsigned long long d ) (since C++20)
   noexcept;
   Forms a std::chrono::day literal representing a day of the month in the calendar.

Parameters
   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);
   }

Notes
   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.

Example

// Run this code
 #include <chrono>
 #include <iostream>

 int main()
 {
     using namespace std::literals::chrono_literals;

     std::cout << static_cast<unsigned>(42d) << '\t' << 42d << '\n'
               << static_cast<unsigned>(256d) << '\t' << 256d << '\n' // unspecified
               << static_cast<unsigned>(298d) << '\t' << 298d << '\n'; // unspecified
 }

Possible output:
 42 42 is not a valid day
 0 00 is not a valid day
 42 42 is not a valid day

See also
   constructor constructs a day
                     (public member function of std::chrono::day)
   operator unsigned retrieves the stored day value
                     (public member function of std::chrono::day)