ceph/src/boost/libs/date_time/xmldoc/ex_seconds_since_epoch.xml

   1 <?xml version="1.0" encoding="utf-8"?>
   2 <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
   3 "../../../tools/boostbook/dtd/boostbook.dtd">
   4
   5 <!-- Copyright (c) 2001-2005 CrystalClear Software, Inc.
   6      Subject to the Boost Software License, Version 1.0.
   7      (See accompanying file LICENSE_1_0.txt or  http://www.boost.org/LICENSE_1_0.txt)
   8 -->
   9
  10 <section id="date_time.examples.seconds_since_epoch">
  11   <title>Seconds Since Epoch</title>
  12
  13   <para>
  14     Example of calculating seconds elapsed since epoch (1970-Jan-1) using local_date_time.
  15   </para>
  16   <programlisting>
  17     <![CDATA[
  18   /* This example demonstrates the use of the time zone database and
  19    * local time to calculate the number of seconds since the UTC
  20    * time_t epoch 1970-01-01 00:00:00.  Note that the selected timezone
  21    * could be any timezone supported in the time zone database file which
  22    * can be modified and updated as needed by the user.
  23    *
  24    * To solve this problem the following steps are required:
  25    * 1) Get a timezone from the tz database for the local time
  26    * 2) Construct a local time using the timezone
  27    * 3) Construct a posix_time::ptime for the time_t epoch time
  28    * 4) Convert the local_time to utc and subtract the epoch time
  29    *
  30    */
  31
  32   #include "boost/date_time/local_time/local_time.hpp"
  33   #include <iostream>
  34
  35   int main()
  36   {
  37     using namespace boost::gregorian;
  38     using namespace boost::local_time;
  39     using namespace boost::posix_time;
  40
  41     tz_database tz_db;
  42     try {
  43       tz_db.load_from_file("../data/date_time_zonespec.csv");
  44     }catch(data_not_accessible dna) {
  45       std::cerr << "Error with time zone data file: " << dna.what() << std::endl;
  46       exit(EXIT_FAILURE);
  47     }catch(bad_field_count bfc) {
  48       std::cerr << "Error with time zone data file: " << bfc.what() << std::endl;
  49       exit(EXIT_FAILURE);
  50     }
  51
  52     time_zone_ptr nyc_tz = tz_db.time_zone_from_region("America/New_York");
  53     date in_date(2004,10,04);
  54     time_duration td(12,14,32);
  55     // construct with local time value
  56     // create not-a-date-time if invalid (eg: in dst transition)
  57     local_date_time nyc_time(in_date,
  58                              td,
  59                              nyc_tz,
  60                              local_date_time::NOT_DATE_TIME_ON_ERROR);
  61
  62     std::cout << nyc_time << std::endl;
  63
  64     ptime time_t_epoch(date(1970,1,1));
  65     std::cout << time_t_epoch << std::endl;
  66
  67     // first convert nyc_time to utc via the utc_time()
  68     // call and subtract the ptime.
  69     time_duration diff = nyc_time.utc_time() - time_t_epoch;
  70
  71     //Expected 1096906472
  72     std::cout << "Seconds diff: " << diff.total_seconds() << std::endl;
  73
  74   }
  75     ]]>
  76   </programlisting>
  77 </section>