id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
9584	date_time::difference produces incorrect values	Alexey Spiridonov <bstbg.20.lesha@…>	Artyom Beilis	"The program below attempts to compute the local timezone's GMT offset for a given timestamp. The idea is simple. First, get the year-month-day-hour-minute-second representation of the timestamp in the local timezone. Then, create a UTC date_time with exactly the same components. The difference between those times is exactly the UTC offset. The program gives this:

{{{
g++ -std=c++11 c.cpp -o c -l boost_locale ; ./c 1383469199 ; ./c 0; 
-25199
-28799
}}}

The expected output is 28800 (8 hours) both times, since my computer's local timezone is America/Los_Angeles (or Pacific Time). 

{{{#!c++
#include <boost/locale.hpp>
#include <iostream>

int compute_utc_offset_seconds(time_t time_since_utc_epoch) {
  using namespace boost::locale;
  std::locale loc = generator()("""");

  // Get the local time coordinates for the given timestamp
  date_time local_dt{(double)time_since_utc_epoch, calendar(loc)};

  // Copy the date_time coordinates into a UTC value
  date_time utc_dt{calendar(loc, ""UTC"")};
  for (auto p : {
    period::year(), period::month(), period::day(),
    period::hour(), period::minute(), period::second()
  }) {
    utc_dt.set(p, local_dt.get(p));
  }
   
  return local_dt.difference(utc_dt, period::second());
}

int main(int argc, char **argv) {
  if (argc < 2) {
    return 1;
  }
  std::cout << compute_utc_offset_seconds(atoi(argv[1])) << std::endl;
  return 0;
}
}}} 
"	Bugs	closed	To Be Determined	locale	Boost 1.54.0	Problem	fixed