can boost gregorian date and boost posix time properly calculate unixtime?

Question

I am trying to write a simple timestamping system that provides epoch seconds and fractional seconds from the current time. I am using boost library and have something like this:

const boost::posix_time::ptime epoch(boost::gregorian::date(1970, 1, 1));
boost::posix_time::ptime time() {
    boost::posix_time::ptime now = boost::posix_time::microsec_clock::universal_time();
    return now;
}
boost::posix_time::time_duration dur = (time() - epoch);

and then use the following elements to extract the epoch values:

dur.total_seconds();
dur.fractional_seconds();

Specifically, will this return a proper unix time? If not, any suggestions as to how to correct it? Thanks.

Answer 1

Yes, that should work, but, to be certain, there's always experimental evidence:

#include <iostream>
#include <time.h>
#include <boost/date_time.hpp>
namespace bpt = boost::posix_time;
namespace bg = boost::gregorian;
int main()
{
    bpt::time_duration dur = bpt::microsec_clock::universal_time()
                           - bpt::ptime(bg::date(1970, 1, 1));
    timespec ts;
    clock_gettime(CLOCK_REALTIME, &ts);
    std::cout << std::setfill('0')
              << " boost: " << dur.total_seconds() << '.' << std::setw(6)
                            << dur.fractional_seconds() << '\n'
              << " ctime: " << time(NULL) << '\n'
              << " posix: " << ts.tv_sec << '.' << std::setw(9)
                            << ts.tv_nsec << '\n';
}

I get

Linux/gcc

 boost: 1361502964.664746
 ctime: 1361502964
 posix: 1361502964.664818326

Sun/Sun Studio

 boost: 1361503762.775609
 ctime: 1361503762
 posix: 1361503762.775661600

AIX/XLC

 boost: 1361503891.342930
 ctime: 1361503891
 posix: 1361503891.342946000

and even Windows/Visual Studio

 boost: 1361504377.084231
 ctime: 1361504377

Looks like they all agree on how many seconds passed since date(1970,1,1)