Hi Jon,
On 11/8/2016 6:28 PM, Jon Zeppieri wrote:
George, these are not correct results. The UTC offset is correct,
but the time fields are not -- under the assumption that you're
trying to round-trip them unchanged. (But maybe that's not a
correct assumption.) At any rate, I think your original example
demonstrates a problem with seconds->date on Windows.
Sorry, that was confusing. What I meant to say was: the results are
correct (given the treatment of the original date fields as UTC and
the treatment of the resulting seconds as local), but based on your
original post, I don't think they're the results you were after. But
I'm not certain of that.
- Jon
What I'm trying to do is the following:
- I'm given 2 datetimes as iso8601 YYYY-MM-DD HH:MM strings, and a time
zone offset
- create UTC datetimes from the strings and tz
- query a database returning records between the 2 UTC datetimes
OK that was pretty easy. I believe I need to get [or look up somehow] a
separate tz for each date string because the range may span both
standard and daylight time, but at least I can get this far.
Now the hard part:
- I need to turn the UTC datetimes on all the results back into local
times with the right time zone
This part is driving me nuts. Nothing seems to work exactly right.
(seconds->date ... #T) seems to get the numbers right, but not always
the timezone, and in any case it is limited to the local timezone of the
machine - useless if local *is* UTC, and since I can't specify an
arbitrary timezone, I can't use it in a server side application.
What I have tried so far amounts to: [reformatted a bit]
(let* [
(tz -4)
(offset (* 60 60 tz))
(d (make-time 'time-duration 0 offset))
(date-in (sql-datetime->srfi-date ... ));; date comes in here
(t1 (date->time-utc date-in))
(t2 (add-duration t1 d))
(date1-lcl (time-utc->date t2 offset))
(date1-utc (time-utc->date t2 0 ))
(t3 (date->seconds date-in))
(t4 (+ t3 offset))
(date2-lcl (seconds->date t4 #t))
(date2-utc (seconds->date t4 #f))
(date3-lcl (date* (date-second date-in)
(date-minute date-in)
(date-hour date-in)
(date-day date-in)
(date-month date-in)
(date-year date-in)
0
0
#f
offset
0
"LCL" ))
(date3-utc (date* (date-second date-in)
(date-minute date-in)
(date-hour date-in)
(date-day date-in)
(date-month date-in)
(date-year date-in)
0
0
#f
0
0
"UTC"
))
]
(printf "UTC input : ~s ~s~n" date-in (date->string date-in "~1
~2"))
(printf "~n")
(printf "srfi tz : ~s ~s~n" date1-lcl (date->string date1-lcl
"~1 ~2"))
(printf "srfi 0 : ~s ~s~n" date1-utc (date->string date1-utc
"~1 ~2"))
(printf "~n")
(printf "s->d #t : ~s ~s~n" date2-lcl (date->string date2-lcl
"~1 ~2"))
(printf "s->d #f : ~s ~s~n" date2-utc (date->string date2-utc
"~1 ~2"))
(printf "~n")
(printf "date* ofst: ~s ~s~n" date3-lcl (date->string date3-lcl
"~1 ~2"))
(printf "date* 0 : ~s ~s~n" date3-utc (date->string date3-utc
"~1 ~2"))
)
=>
UTC input : #(struct:date* 0 0 4 12 11 2016 6 316 #f 0 0 "") "2016-11-12
04:00:00Z"
srfi tz : #(struct:date* 0 0 20 11 11 2016 5 315 #f -14400 0 "")
"2016-11-11 20:00:00-0400"
srfi 0 : #(struct:date* 0 0 0 12 11 2016 6 316 #f 0 0 "")
"2016-11-12 00:00:00Z"
s->d #t : #(struct:date* 0 0 0 12 11 2016 6 316 #t -14400 0 "Eastern
Daylight Time") "2016-11-12 00:00:00-0400"
s->d #f : #(struct:date* 0 0 5 12 11 2016 6 316 #f 0 0
"UTC") "2016-11-12 05:00:00Z"
date* ofst: #(struct:date* 0 0 4 12 11 2016 0 0 #f -14400 0 "LCL")
"2016-11-12 04:00:00-0400"
date* 0 : #(struct:date* 0 0 4 12 11 2016 0 0 #f 0 0 "UTC")
"2016-11-12 04:00:00Z"
I've been thinking I should look into Gregor, but a brief skimming of
its docs was daunting.
George
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