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

["Jeffrey R. Carter" <spam.jrcarter.not@nospam.acm.org>]

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