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> 78