Re: Advice on Calendar.Time

[Keith Thompson <kst-u@mib.org>]

Jacob Sparre Andersen <sparre@nbi.dk> writes:
> Keith Thompson wrote:
>> That might be acceptable for an embedded system.  If it's a
>> user-oriented OS (like, say, Unix or Windows), making the system
>> clock incorrect by an hour for half of each year would be a very bad
>> idea.
>
> Unix systems (at least those I have used) do actually by default run
> the system clock on UTC without fiddling around with the hours twice a
> year.  It is only the time shown to the users which is changed
> (depending on where in the world they claim to be located).

Right, and the Unix approach is, IMHO, exactly the right one (ignoring
any leap-second issues).  The problem is that Ada.Calendar on
Unix-like systems typically uses local time, i.e., the system UTC
clock adjusted by any system-defined or user-defined time zone offset,
with no mechanism for going back to the underlying UTC time.

(I'm amplifying on what you wrote, not disagreeing with it.)

>> On some systems, time zone information has a default system-wide
>> value, but can be changed for individual processes.  Setting the $TZ
>> environment variable to "UTC" certainly isn't portable, but it might
>> be good enough for the OP's purposes.
>
> Fixing the Ada.Calendar system so you can request both UTC and "user
> time" would be the right solution.  I hope this is done in Ada2005.

I believe there are proposals to do just that.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center             <*>  <http://users.sdsc.edu/~kst>
We must do something.  This is something.  Therefore, we must do this.