the hour of a date-and-time object
Returned values are in the range 0 to 23.
| std::year_of | the calendar year of a date-and-time object |
| std::month_of | the month of a date-and-time object |
| std::day_of | the day of a month of a date-and-time object |
| std::day_of_week_of | the day of the week of a date-and-time object |
| std::minute_of | the minute of an hour of a date-and-time object |
| std::second_of | the second of a minute of a date-and-time object |
| std::time_shift_of |
| std_types::date_and_time | returns the hour of the day |