[date_time] dst_local_start_time
Hello I'm confused about the returned time of the dst_local_start_time() function. First of all I don't understand why a ptime is returned and not a local_date_time, buy anyway. The ptime I get returned for the timezone Europe/Zurich for 2007 is: 2007-Mar-25 02:00:00 Assuming that this is a UTC time, the local time in Zurich would then be 2007-Mar-25 04:00:00 (because during summertime, Zurich is 2h ahead of UTC), but the correct local dst start time would be 2007-Mar-25 03:00:00 (because the clocks are shifted from 2 to 3). To correctly calculate the dst start time, I have to add the dst_offset to the returned time_of_day. The returned ptime 2007-Mar-25 02:00:00 seems to be the endtime of wintertime as a local time. time_zone_ptr zh_tz = tz_db.time_zone_from_region("Europe/Zurich"); ptime zh_dst_start_time = zh_tz->dst_local_start_time(2007); std::cout << zh_dst_start_time << std::endl; // 2007-Mar-25 02:00:00 local_date_time zh_dst_local_start_time = local_date_time(zh_dst_start_time, zh_tz); std::cout << zh_dst_local_start_time << std::endl; // 2007-Mar-25 04:00:00 CEST which is wrong! ptime zh_dst_start_time_ok = zh_dst_start_time + zh_tz->dst_offset(); local_date_time zh_dst_local_start_time_ok = local_date_time(zh_dst_start_time_ok.date(), zh_dst_start_time_ok.time_of_day(), zh_tz, true); std::cout << zh_dst_local_start_time_ok << std::endl; // 2007-Mar-25 03:00:00 CEST which is correct So what time exactly is local_start_time() returning? Is this a bug or am I missing something? Regards James
Hi, I had a similar problem in getting the current wall time in New York. I wrote the following working function and added a bunch of comments, since the library is counter-intuitive here IMHO: // Get local time of day, based on time zone const boost::posix_time::time_duration DateTime::localizedTimeOfDayAsDuration(const boost::local_time::time_zone_ptr timeZone) { /* This looks a bit perverted (and it is in my eyes :-)) Calling time_of_day on a local_date_time object implicitly turns it into a UTC ptime object first, thus yielding UTC time_of_day instead of the wall time (I do not really understand why it works this way, but it does). Calling local_time on a local_date_time object returns a ptime object which in this case represents wall time within the given time zone (again, I don't know why the behavior is this way, but it is). */ return local_microsec_clock::local_time(timeZone).local_time().time_of_day(); } Please let me know if that helped or if you found a better solution/explanation. Regards, Roland Jean-Pierre Bergamin wrote:
Hello
I'm confused about the returned time of the dst_local_start_time() function. First of all I don't understand why a ptime is returned and not a local_date_time, buy anyway.
The ptime I get returned for the timezone Europe/Zurich for 2007 is: 2007-Mar-25 02:00:00 Assuming that this is a UTC time, the local time in Zurich would then be 2007-Mar-25 04:00:00 (because during summertime, Zurich is 2h ahead of UTC), but the correct local dst start time would be 2007-Mar-25 03:00:00 (because the clocks are shifted from 2 to 3). To correctly calculate the dst start time, I have to add the dst_offset to the returned time_of_day.
The returned ptime 2007-Mar-25 02:00:00 seems to be the endtime of wintertime as a local time.
time_zone_ptr zh_tz = tz_db.time_zone_from_region("Europe/Zurich"); ptime zh_dst_start_time = zh_tz->dst_local_start_time(2007); std::cout << zh_dst_start_time << std::endl; // 2007-Mar-25 02:00:00 local_date_time zh_dst_local_start_time = local_date_time(zh_dst_start_time, zh_tz); std::cout << zh_dst_local_start_time << std::endl; // 2007-Mar-25 04:00:00 CEST which is wrong!
ptime zh_dst_start_time_ok = zh_dst_start_time + zh_tz->dst_offset(); local_date_time zh_dst_local_start_time_ok = local_date_time(zh_dst_start_time_ok.date(), zh_dst_start_time_ok.time_of_day(), zh_tz, true); std::cout << zh_dst_local_start_time_ok << std::endl; // 2007-Mar-25 03:00:00 CEST which is correct
So what time exactly is local_start_time() returning? Is this a bug or am I missing something?
Regards
James _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Hi, forgot to write some kind of conclusion after my code sample: My guess: The dst_local_start_time() function returns a ptime object which actually represents wall time at the location (Zurich in your case). I would say that 2007-Mar-25 02:00:00 is the start of the DST just like 2007-Mar-25 03:00:00, because those two times are exactly the same. It's not like "when the clock reaches 02:00, we've reached end of wintertime, then we switch to 03:00 and have beginning of summertime". On that day, in the infinitesimal time interval when it is 02:00, it is also 03:00. So, personally, I would say, the confusing part is that local times are represented by ptimes in some cases (see also the example I sent). The result is OK, though. If you look at the dst_local_end_time(), it is consistent with the start function: In both cases, it returns the time which would be shown on the clock without the switch. Regards, Roland Roland Bock wrote:
Hi,
I had a similar problem in getting the current wall time in New York. I wrote the following working function and added a bunch of comments, since the library is counter-intuitive here IMHO:
// Get local time of day, based on time zone const boost::posix_time::time_duration DateTime::localizedTimeOfDayAsDuration(const boost::local_time::time_zone_ptr timeZone) { /* This looks a bit perverted (and it is in my eyes :-))
Calling time_of_day on a local_date_time object implicitly turns it into a UTC ptime object first, thus yielding UTC time_of_day instead of the wall time (I do not really understand why it works this way, but it does).
Calling local_time on a local_date_time object returns a ptime object which in this case represents wall time within the given time zone (again, I don't know why the behavior is this way, but it is). */ return local_microsec_clock::local_time(timeZone).local_time().time_of_day(); }
Please let me know if that helped or if you found a better solution/explanation.
Regards,
Roland
Jean-Pierre Bergamin wrote:
Hello
I'm confused about the returned time of the dst_local_start_time() function. First of all I don't understand why a ptime is returned and not a local_date_time, buy anyway.
The ptime I get returned for the timezone Europe/Zurich for 2007 is: 2007-Mar-25 02:00:00 Assuming that this is a UTC time, the local time in Zurich would then be 2007-Mar-25 04:00:00 (because during summertime, Zurich is 2h ahead of UTC), but the correct local dst start time would be 2007-Mar-25 03:00:00 (because the clocks are shifted from 2 to 3). To correctly calculate the dst start time, I have to add the dst_offset to the returned time_of_day.
The returned ptime 2007-Mar-25 02:00:00 seems to be the endtime of wintertime as a local time.
time_zone_ptr zh_tz = tz_db.time_zone_from_region("Europe/Zurich"); ptime zh_dst_start_time = zh_tz->dst_local_start_time(2007); std::cout << zh_dst_start_time << std::endl; // 2007-Mar-25 02:00:00 local_date_time zh_dst_local_start_time = local_date_time(zh_dst_start_time, zh_tz); std::cout << zh_dst_local_start_time << std::endl; // 2007-Mar-25 04:00:00 CEST which is wrong!
ptime zh_dst_start_time_ok = zh_dst_start_time + zh_tz->dst_offset(); local_date_time zh_dst_local_start_time_ok = local_date_time(zh_dst_start_time_ok.date(), zh_dst_start_time_ok.time_of_day(), zh_tz, true); std::cout << zh_dst_local_start_time_ok << std::endl; // 2007-Mar-25 03:00:00 CEST which is correct
So what time exactly is local_start_time() returning? Is this a bug or am I missing something?
Regards
James _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Hello We ended up with an explanation like this as well. But in my opinion, 2:00 in summertime does not exist, since 2:00 is 3:00. I'd expect that the function dst_local_start_time returns a local_date_time of 2007-Mar-25 03:00:00. As you say, some functions with local_date_times behave very "unnatural" and counterintuitive. Does it make sense to file a bug-report? Regards James
forgot to write some kind of conclusion after my code sample:
My guess: The dst_local_start_time() function returns a ptime object which actually represents wall time at the location (Zurich in your case).
I would say that 2007-Mar-25 02:00:00 is the start of the DST just like 2007-Mar-25 03:00:00, because those two times are exactly the same. It's not like "when the clock reaches 02:00, we've reached end of wintertime, then we switch to 03:00 and have beginning of summertime". On that day, in the infinitesimal time interval when it is 02:00, it is also 03:00.
So, personally, I would say, the confusing part is that local times are represented by ptimes in some cases (see also the example I sent). The result is OK, though.
If you look at the dst_local_end_time(), it is consistent with the start function: In both cases, it returns the time which would be shown on the clock without the switch.
Regards,
Roland
Roland Bock wrote:
Hi,
I had a similar problem in getting the current wall time in New York. I wrote the following working function and added a bunch of comments, since the library is counter-intuitive here IMHO:
// Get local time of day, based on time zone const boost::posix_time::time_duration DateTime::localizedTimeOfDayAsDuration(const boost::local_time::time_zone_ptr timeZone) { /* This looks a bit perverted (and it is in my eyes :-))
Calling time_of_day on a local_date_time object implicitly turns it into a UTC ptime object first, thus yielding UTC time_of_day instead of the wall time (I do not really understand why it works this way, but it does).
Calling local_time on a local_date_time object returns a ptime object which in this case represents wall time within the given time zone (again, I don't know why the behavior is this way, but it is). */ return local_microsec_clock::local_time(timeZone).local_time().time_of_day(); }
Please let me know if that helped or if you found a better solution/explanation.
Regards,
Roland
Jean-Pierre Bergamin wrote:
Hello
I'm confused about the returned time of the dst_local_start_time() function. First of all I don't understand why a ptime is returned and not a local_date_time, buy anyway.
The ptime I get returned for the timezone Europe/Zurich for 2007 is: 2007-Mar-25 02:00:00 Assuming that this is a UTC time, the local time in Zurich would then be 2007-Mar-25 04:00:00 (because during summertime, Zurich is 2h ahead of UTC), but the correct local dst start time would be 2007-Mar-25 03:00:00 (because the clocks are shifted from 2 to 3). To correctly calculate the dst start time, I have to add the dst_offset to the returned time_of_day.
The returned ptime 2007-Mar-25 02:00:00 seems to be the endtime of wintertime as a local time.
time_zone_ptr zh_tz = tz_db.time_zone_from_region("Europe/Zurich"); ptime zh_dst_start_time = zh_tz->dst_local_start_time(2007); std::cout << zh_dst_start_time << std::endl; // 2007-Mar-25 02:00:00 local_date_time zh_dst_local_start_time = local_date_time(zh_dst_start_time, zh_tz); std::cout << zh_dst_local_start_time << std::endl; // 2007-Mar-25 04:00:00 CEST which is wrong!
ptime zh_dst_start_time_ok = zh_dst_start_time + zh_tz->dst_offset(); local_date_time zh_dst_local_start_time_ok = local_date_time(zh_dst_start_time_ok.date(), zh_dst_start_time_ok.time_of_day(), zh_tz, true); std::cout << zh_dst_local_start_time_ok << std::endl; // 2007-Mar-25 03:00:00 CEST which is correct
So what time exactly is local_start_time() returning? Is this a bug or am I missing something?
Regards
James _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Hi, regarding 2:00 or 3:00: I can live with both. Maybe there is an official definition? The more important thing is to document the exact meaning of the return value. Thus, a bug report for the documentation would be useful. Regarding "unnatural" behaviour: The short-term change would be to add more documentation. In the long run, I would vote for modifying the API. Again, a bug report would be useful. Regards, Roland Jean-Pierre Bergamin wrote:
Hello
We ended up with an explanation like this as well. But in my opinion, 2:00 in summertime does not exist, since 2:00 is 3:00. I'd expect that the function dst_local_start_time returns a local_date_time of 2007-Mar-25 03:00:00.
As you say, some functions with local_date_times behave very "unnatural" and counterintuitive. Does it make sense to file a bug-report?
Regards
James
forgot to write some kind of conclusion after my code sample:
My guess: The dst_local_start_time() function returns a ptime object which actually represents wall time at the location (Zurich in your case).
I would say that 2007-Mar-25 02:00:00 is the start of the DST just like 2007-Mar-25 03:00:00, because those two times are exactly the same. It's not like "when the clock reaches 02:00, we've reached end of wintertime, then we switch to 03:00 and have beginning of summertime". On that day, in the infinitesimal time interval when it is 02:00, it is also 03:00.
So, personally, I would say, the confusing part is that local times are represented by ptimes in some cases (see also the example I sent). The result is OK, though.
If you look at the dst_local_end_time(), it is consistent with the start function: In both cases, it returns the time which would be shown on the clock without the switch.
Regards,
Roland
Roland Bock wrote:
Hi,
I had a similar problem in getting the current wall time in New York. I wrote the following working function and added a bunch of comments, since the library is counter-intuitive here IMHO:
// Get local time of day, based on time zone const boost::posix_time::time_duration DateTime::localizedTimeOfDayAsDuration(const boost::local_time::time_zone_ptr timeZone) { /* This looks a bit perverted (and it is in my eyes :-))
Calling time_of_day on a local_date_time object implicitly turns it into a UTC ptime object first, thus yielding UTC time_of_day instead of the wall time (I do not really understand why it works this way, but it does).
Calling local_time on a local_date_time object returns a ptime object which in this case represents wall time within the given time zone (again, I don't know why the behavior is this way, but it is). */ return local_microsec_clock::local_time(timeZone).local_time().time_of_day(); }
Please let me know if that helped or if you found a better solution/explanation.
Regards,
Roland
Jean-Pierre Bergamin wrote:
Hello
I'm confused about the returned time of the dst_local_start_time() function. First of all I don't understand why a ptime is returned and not a local_date_time, buy anyway.
The ptime I get returned for the timezone Europe/Zurich for 2007 is: 2007-Mar-25 02:00:00 Assuming that this is a UTC time, the local time in Zurich would then be 2007-Mar-25 04:00:00 (because during summertime, Zurich is 2h ahead of UTC), but the correct local dst start time would be 2007-Mar-25 03:00:00 (because the clocks are shifted from 2 to 3). To correctly calculate the dst start time, I have to add the dst_offset to the returned time_of_day.
The returned ptime 2007-Mar-25 02:00:00 seems to be the endtime of wintertime as a local time.
time_zone_ptr zh_tz = tz_db.time_zone_from_region("Europe/Zurich"); ptime zh_dst_start_time = zh_tz->dst_local_start_time(2007); std::cout << zh_dst_start_time << std::endl; // 2007-Mar-25 02:00:00 local_date_time zh_dst_local_start_time = local_date_time(zh_dst_start_time, zh_tz); std::cout << zh_dst_local_start_time << std::endl; // 2007-Mar-25 04:00:00 CEST which is wrong!
ptime zh_dst_start_time_ok = zh_dst_start_time + zh_tz->dst_offset(); local_date_time zh_dst_local_start_time_ok = local_date_time(zh_dst_start_time_ok.date(), zh_dst_start_time_ok.time_of_day(), zh_tz, true); std::cout << zh_dst_local_start_time_ok << std::endl; // 2007-Mar-25 03:00:00 CEST which is correct
So what time exactly is local_start_time() returning? Is this a bug or am I missing something?
Regards
James _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
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Roland Bock