Re: [Boost-users] [date_time] local_time_period between two different time zones

From: Raúl Huertas (raulh39_at_[hidden])
Date: 2006-11-16 15:09:58

Alberto Giannetti escribió:
> I want to calculate the time difference between local_date_time objects that I
> initialized using two different time zones:
>
> ...
>
>   time_zone_ptr tzp_nyc = tz_db.time_zone_from_region("America/New_York");
>   time_zone_ptr tzp_rome = tz_db.time_zone_from_region("Europe/Rome");
>
>   local_date_time nyc_time(second_clock::universal_time(), tzp_nyc);  // #1
> ...
>   local_date_time rome_time(second_clock::universal_time(), tzp_rome); // #2
> ...
>
> tdiff.lenth() returns 00:00:00. Why the function can't return the difference
> between the two local times?
>
>
>   

I don't even read the Boost.Date_Time documentation, so maybe my 
response is going to be a nonsense, but nobody is answering, so I'll 
give it a try...

I think that second_clock::universal_time() is returning the same time 
in lines #| and #2. Your computer clock is the same, whether you are in 
New York or in Rome.

It is when you call to_simple_string(...local_time()) when this same 
time gets represented as NewYork time or Rome time. Now in Roma it is 
21:00 h, but in New York it is 15:00. The universal time it's the same, 
but gets "changed" when you call to_simple_string.

So if you try to diff the two times, you get 00:00:00.

It seems logical to me... ;)

Hope it helps (and excuse my poor English),
Raul.