| <?xml version="1.0" encoding="utf-8"?> |
| <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN" |
| "../../../tools/boostbook/dtd/boostbook.dtd"> |
| |
| <!-- Copyright (c) 2001-2005 CrystalClear Software, Inc. |
| Subject to the Boost Software License, Version 1.0. |
| (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) |
| --> |
| |
| <section id="date_time.examples.seconds_since_epoch"> |
| <title>Seconds Since Epoch</title> |
| |
| <para> |
| Example of calculating seconds elapsed since epoch (1970-Jan-1) using local_date_time. |
| </para> |
| <programlisting> |
| <![CDATA[ |
| /* This example demonstrates the use of the time zone database and |
| * local time to calculate the number of seconds since the UTC |
| * time_t epoch 1970-01-01 00:00:00. Note that the selected timezone |
| * could be any timezone supported in the time zone database file which |
| * can be modified and updated as needed by the user. |
| * |
| * To solve this problem the following steps are required: |
| * 1) Get a timezone from the tz database for the local time |
| * 2) Construct a local time using the timezone |
| * 3) Construct a posix_time::ptime for the time_t epoch time |
| * 4) Convert the local_time to utc and subtract the epoch time |
| * |
| */ |
| |
| #include "boost/date_time/local_time/local_time.hpp" |
| #include <iostream> |
| |
| int main() |
| { |
| using namespace boost::gregorian; |
| using namespace boost::local_time; |
| using namespace boost::posix_time; |
| |
| tz_database tz_db; |
| try { |
| tz_db.load_from_file("../data/date_time_zonespec.csv"); |
| }catch(data_not_accessible dna) { |
| std::cerr << "Error with time zone data file: " << dna.what() << std::endl; |
| exit(EXIT_FAILURE); |
| }catch(bad_field_count bfc) { |
| std::cerr << "Error with time zone data file: " << bfc.what() << std::endl; |
| exit(EXIT_FAILURE); |
| } |
| |
| time_zone_ptr nyc_tz = tz_db.time_zone_from_region("America/New_York"); |
| date in_date(2004,10,04); |
| time_duration td(12,14,32); |
| // construct with local time value |
| // create not-a-date-time if invalid (eg: in dst transition) |
| local_date_time nyc_time(in_date, |
| td, |
| nyc_tz, |
| local_date_time::NOT_DATE_TIME_ON_ERROR); |
| |
| std::cout << nyc_time << std::endl; |
| |
| ptime time_t_epoch(date(1970,1,1)); |
| std::cout << time_t_epoch << std::endl; |
| |
| // first convert nyc_time to utc via the utc_time() |
| // call and subtract the ptime. |
| time_duration diff = nyc_time.utc_time() - time_t_epoch; |
| |
| //Expected 1096906472 |
| std::cout << "Seconds diff: " << diff.total_seconds() << std::endl; |
| |
| } |
| ]]> |
| </programlisting> |
| </section> |