From cppreference.com
classday;(since C++20)The class day represents a day in a month. Its normal range is [1, 31], but it may hold any number in [0, 255].
day is a
.
Member functions
Nonmember functions
Helper classes
Literals
Defined in inline namespace std::literals::chrono_literals
(C++20)
a std::chrono::day literal representing a day of a month
(function)