Re: [Boost-users] [date_time]time zone input

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-10-01 20:03:59

Sean Huang wrote:

>> then the constructed timezone would have no information about the true 
>> nature
>> of the timezone.  So now if you say
>>
>>  ldt += months(5);
>>
>> the only possible assumption the library can make is that there is no 
>> daylight
>> savings -- it is only aware of the UTC offset.  This sort of assumption
>> doesn't work for a good percentage of the world, so it's a dangerous
>> assumption for the library to make.
> Thanks for the detailed explanation. I have not done much work on date/time 
> so I 'll take your word for it. On the other hand, I'm still not totally 
> convinced this is such a bad assumption to make (or should we make it a 
> convention :-)). If people do ldt+= months(5), ldt still has the right time. 

No, that's the point.  It will be an incorrectly adjusted time....off by an hour.

> It only causes confusion if ldt is displayed without a time-zone offset. 
> Also, because %q/Q is supported for output (for example, your ISO format 
> example in the documentation),  shouldn't there be corresponing input 
> support for symmetry?

It's documented as not symmetric for the reasons above.

>> as hard as it sounds, a custom timezone type, etc)....so maybe you can 
>> give me
>> a bit more context on your app and I can point you to a 'less messy' 
>> workaround.
> That would be great. What we are trying to do is to convert DICOM DT (Date 
> time) element to boost::date_time and it is in the format shown below:
> YYYYMMDDHHMMSS.FFFFFF&ZZZZ
> One way I can think of is treat the string as posix time and parse the 
> time-zone offset part ourselves. It sounds like there are better ways to 
> accomplish this. I would appreciate it very much if you could point me to 
> the right direction.

That's exactly what I would suggest, although actually you can probably parse 
it into a time_duration. What are you going to do with the timezone offset 
once you get it?  Do you need it for anything or do you just do a one time 
adjustment?

Jeff