Simplest way to get current time in current timezone using boost::date_time?

If I do date +%H-%M-%S on the commandline (Debian/Lenny), I get a user-friendly (not UTC, not DST-less, the time a normal person has on their wristwatch) time printed.

What's the simplest way to obtain the same thing with boost::date_time ?

If I do this:

std::ostringstream msg;

boost::local_time::local_date_time t = 
  boost::local_time::local_sec_clock::local_time(
    boost::local_time::time_zone_ptr()
  );

boost::local_time::local_time_facet* lf(
  new boost::local_time::local_time_facet("%H-%M-%S")
);

msg.imbue(std::locale(msg.getloc(),lf));
msg << t;

Then msg.str() is an hour earlier than the time I want to see. I'm not sure whether this is because it's showing UTC or local timezo开发者_开发百科ne time without a DST correction (I'm in the UK).

What's the simplest way to modify the above to yield the DST corrected local timezone time ? I have an idea it involves boost::date_time:: c_local_adjustor but can't figure it out from the examples.

This does what I want:

  namespace pt = boost::posix_time;
  std::ostringstream msg;
  const pt::ptime now = pt::second_clock::local_time();
  pt::time_facet*const f = new pt::time_facet("%H-%M-%S");
  msg.imbue(std::locale(msg.getloc(),f));
  msg << now;

While this is not using boost::date_time it's relatively easy with boost::locale, which is quite more adapted for this task. As your need is simply getting a formatted time from the current locale.

IMHO boost::date_time should be used when you deal with softwares like gantt/planning computations, were you have alot of date_time arithmetic. But simply for using time and doing some arithmetic on it, you will faster success with boost::locale.

#include <iostream>
#include <boost/locale.hpp>

using namespace boost;

int main(int argc, char **argv) {
   locale::generator gen;
   std::locale::global(gen(""));

   locale::date_time now;
   std::cout.imbue(std::locale());       
   std::cout << locale::as::ftime("%H-%M-%S") << now << std::endl;

   return 0;
}

Right now it should output : 15-45-48. :)

I haven't found other answers to be convenient enough, so here is an example that showcases how to get a local or universal time with full control of units:

#include <boost/date_time/local_time/local_time.hpp>
#include <boost/format.hpp>

#include <iostream>

int main()
{
    auto const now = boost::posix_time::microsec_clock::local_time(); // or universal_time() for GMT+0
    if (now.is_special()) {
        // some error happened
        return 1;
    }

    // example timestamp (eg for logging)
    auto const t = now.time_of_day();
    boost::format formater("[%02d:%02d:%02d.%06d]");
    formater % t.hours() % t.minutes() % t.seconds() % (t.total_microseconds() % 1000000);
    std::cout << formater.str();
}

Note: the time_of_day struct has no .microseconds() or .nanoseconds() functions, there is only .fractional_seconds() which returns an integer that is a multiple of configuration-dependent unit. .num_fractional_digits() can be used to obtain precision information where 10 ^ frac_digits is the number of fractional_seconds that is equal to 1 second.

To obtain configuration-independent sub-second units one can perform modulo with the total_ milli/micro/nano _seconds() functions as a workaround.