std::chrono::day
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  <chrono>
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|   class day;  | 
(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 TriviallyCopyable StandardLayoutType.
Member functions
  constructs a day (public member function)  | |
|    increments or decrements the day   (public member function)  | |
|    adds or subtracts a number of days   (public member function)  | |
|    retrieves the stored day value   (public member function)  | |
|    checks if the stored day value is in the normal range   (public member function)  | 
Nonmember functions
   compares two day objects  (function)  | |
   adds or subtracts a number of days and a day, or find the difference between two days  (function)  | |
   outputs a day into a stream  (function template)  | |
   outputs a day into a stream according to the provided format  (function template)  | |
   parses a day from a stream according to the provided format   (function template)  | 
Literals
|   Defined in inline namespace  
std::literals::chrono_literals  | |
|    (C++20)  | 
   A std::chrono::day literal representing a day of a month    (function)  |