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