Re: Newbie Q: How to program in UTC (time/calendar) ?

[reinkor <reinkor@gmail.com>]

Thanks for clarifying.

I thought "Offset" was reletive to UTC - not relative
to the "local" time.

So

   Time1 := Value("1970-01-01 00:00:00",Time_Zone => UTC_Time_Offset);

gives UTC for the local "input" time "1970-01-01 00:00:00" ?

How do I best "input"/enter UTC time (so a reader of the program
also understand it - an independent of the computer local time)?

reinert

On 27 Mar, 18:58, "Jeffrey R. Carter"
<spam.jrcarter....@nospam.acm.org> wrote:
> reinkor wrote:
> >    Time1 := Value("1970-01-01 00:00:00");
> >    Put(Image(Time1));New_Line;
> >    Put(Image(Ada.Calendar.Time_Of(1970,1,1,Duration(0))));
>
> > 1970-01-01 00:00:00
> > 1969-12-31 23:00:00
>
> > The last output line here reflects the fact that Ada takes
> > "local time" from the computer - and the result would be
> > different if I wait to run my program till next Monday
> > (this weekend we change to summer daylight saving time).
>
> No. It reflects the fact that Image takes an Ada.Calendar.Time_Zones.Time_Offset
> parameter (Time_Zone) that defaults to 0 (UTC). Image is therefore converting
> the supplied time from your computer's offset
> (Ada.Calendar.Time_Zones.UTC_Time_Offset) to the default offset of 0. Your
> offset seems to be 60 (GMT + 1 hr). To get the image of what you passed to it,
> you must specify an offset of UTC_Time_Offset.
>
> The 1st value comes out as expected because Value also takes an
> Ada.Calendar.Time_Zones.Time_Offset parameter (Time_Zone) that defaults to 0
> (UTC). It is therefore taking the supplied string, interpreting it as a time in
> UTC, and converting it to the corresponding time for your computer's offset
> (UTC_Time_Offset). When you pass this time to Image with the default for
> Time_Zone, the conversion is then reversed as described above.
>
> You can compare the representations provided by Image with the values obtained
> by Ada.Calendar.Split to observe the conversions that the operations in
> Ada.Calendar.Formatting perform.
>
> Two comments on your code: "with Ada.Calendar.Formatting;" makes Ada,
> Ada.Calendar, and Ada.Calendar.Formatting visible; there is no need to also with
> Ada.Calendar.
>
> I cannot understand why you would say "Duration (0)" when "0.0" is clearer and
> shorter.
>
> --
> Jeff Carter
> "My mind is a raging torrent, flooded with rivulets of
> thought, cascading into a waterfall of creative alternatives."
> Blazing Saddles
> 89