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

Question

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 timezone 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.

Solution 1

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;

Solution 2

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. :)

Comments

[std''OrgnlDave]

He said a simple way. There is no simple way with Boost date/time. They abstracted and generalized too much.

[timday]

I think that's a little harsh (although not completely unjustified). The above is simple enough (although verbose with all the namespacing). The problem is often more the documentation is telling you how to get to Alpha Centauri when you just wanted to walk around the block. On the other hand, I wanted to do the same thing in Python a while ago, and that didn't need a post on StackOverflow to work out.

[std''OrgnlDave]

don't get me started on my first experience with boost's 'posix time' and how easy I thought it would be to get a POSIX time stamp out of it and how wrong I was! with that said we'd all be lost without Boost

[CashCow]

What you have done will also be very inefficient if you are going to printing a lot of times. And it's a very common error I see. Create the facet and locale once, store it as a static and then start from the imbue() when you have something to print with it.