Re: [Boost-users] Using boost::date_time for timezones

Jeff, Thanks for your reply. I'm afraid I will have to find another solution short-term but look forward to helping try out some of the betas in the future. C++ has been aching for a definitive date-time library - what are the current leaders? re: tz database, it would be helpful to support caching the db results in memory to avoid accidental/lazy implementations going to disk each time. Thanks, Duncan Jeff Garland wrote:

On Wed, 18 Aug 2004 20:33:10 +0100, Duncan Woods wrote

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Hello All,

I'm new to Boost and interested in using it for timezone conversions but I'm not finding it terribly clear. An example, which works fine, uses something of the form:

typedef boost::date_time::local_adjustor us_eastern;

Yes, this allows you to build static converters for a small number of time zones with well defined rules. If there isn't a rule set in the library that suits your application you would need to create one of your own. Since this is totally undocumented, I'll help you if you really want to go this way.

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1. My problem is that I wish to use DST settings other than US and found definitions such as eu_dst_trait in local_timezone_defs.hpp but these seem unused and unusable. Would it require implementation of dst_rules.hpp type classes? If so, Boost would not give much advantage.

I agree date_time doesn't support local time adjustments well...yet.

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2. I would also have liked to specify dst & timezone combinations at run-time which dynamic_local_time_adjustor sounds like it might do - but it appears to have no members.

It has members. Look at the bottom of libs/date_time/test/posix_time/testlocal_adjustor.cpp. Note the comment: //still experimental

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3. Will date_time use the 'tz database' in the future?

The short answer is yes and I expect it before 1.33.

The long answer is that in future releases there will be a generic time_zone class that encapsulates the glob of interfaces that the library needs to correctly handle a time zone. The abstraction will use subclassing to support different concrete time zone implementations. We have a working prototype now that uses Posix timezone strings to construct. So you can do something like:

posix_time_zone arizona_tz("MST-07"); posix_time_zone ny_tz("EST-05EDT,M4.1.0,M10.5.0");

We are working on a variant that will use data from the TZ database so you can say something like boost::shared_ptr tz(tz_database.find("America/New York"));

What we are NOT planning to do is supporting all the historic timezones of the timezone database -- doesn't seem like it's worth the complication. We also are not planning on reading the TZ database binary format directly (it's a directory with binary files for each timezone for those that don't know). Rather we are looking at condensing the contents (probably fron VCALENDAR form) down to a single csv file that can be read in by the application and can be modified as need be using text editors, excel, etc. So in your app it would look something like: tz_database db("zones.csv"); boost::shared_ptr tz(db.find("America/New York"));

Of course this comes with a new local_time class that can use time zones natively to adjust, do calculations, input/output, etc. So in particular, I expect to be able to write the following kind of code tz_database db("zones.csv"); boost::shared_ptr tz(db.find("America/New York")); local_date_time ny_time = second_clock::local_time(tz); //2004-Aug-18 05:27:00 EDT std::cout << "The current time in New York is: " << ny_time << std::endl;

HTH,

Jeff

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