encode/decode-universal-time - reolved - not a bug

[Navid]

I expected the following function to return the correct day of the week, but it is off by one day (reports the previous weekday). The date decreases by one day during the process.

SBCL version 2.2.6, Windows x64

(defun weekday-of (day month year)
  "Return day of the week for a date."
  (nth-value 6
      (decode-universal-time (encode-universal-time 0 0 0 day month year 0))))

E.g.
(weekday-of 3 7 2022) => 5 (but should return 6 as July 3, 2022 is a Sunday).

Thank you for your attention.

Navid

[Navid (jnmadani)]

Looks like this is localization-related. With time-zone adjustment, the result is correct. If I use:

(encode-universal-time 0 0 0 day month year 5)

to account for my GMT-5 time-zone, I get the correct date.

Sorry for the trouble, but it does not appear that I can close/resolve the report.

[Stas Boukarev (stassats)]

I might be better to supply the same timezone to decode-universal-time instead, i.e:

(defun weekday-of (day month year)
  "Return day of the week for a date."
  (nth-value 6
             (decode-universal-time (encode-universal-time 0 0 0 day month year 0) 0)))

[Navid (jnmadani)]

Indeed, thank you!