Unicode Date Formats, YYYY?!
YYYY and yyyy are Unicode date format patterns. These offer quite a bit more flexibility than the old str[fp]time(3) formats, particularly in choosing different representations of the same value (e.g., “September” vs “Sep” vs “09” vs “9”).
- YYYY is defined as the “year for week-of-year”: that is, the year for ISO week dates.
- yyyy is defined as the calendar year.
You probably want the latter.
Update (2018-12-27): See also: Dave DeLong and Erica Sadun.
