date（）仅从日期格式YYYY-00-00开始

Question

I try to do this echo date("Y", strtotime("1999-00-00")); but instead of 1999 it returns 1998. Is there a way how to handle this? I would prefer a "clean way", not something like $finalYear = (float)$year+1 etc. The date format MUST be YYYY-00-00 (with zeros)

Answer 1

If you're absolutely sure that the date's format will never change, you'd be better off with

echo substr('1999-00-00', 0, 4);

rather than incurring the heavy overhead of strtotime() and roundtripping through the entire date/time subsystem.

When you tell PHP's date functions that the month/day are 0, which are "invalid", it'll convert those to the appropriate "previous" values.

e.g.

1999-00-10 is actually 1998-12-10
1999-11-00 is actually 1999-10-31

and so on. It's like saying "yesterday" or "last month". similarly, specifying month 13 makes it

1999-13-01 is actually 2000-01-01