引数originalが表す日付・時刻のsec秒後の日付・時刻を表す構造体。
A structure that represents a date and time
that is sec s later than the date and time
expressed by the argument original.
この例では変数date_loopを
2019/01/01 00:00:00から2022/12/31 00:00:00まで
1日(86400秒)ずつずらしながらループ処理を行う。
In this example, a loop-based processing is performed
with variable date_loop,
which varies from 2019/01/01 00:00:00 to 2022/12/31 00:00:00
at increments of 1 day (86400 s).