Question

Are boost ptime instances always UTC? I can’t see any time zone info on them.

Answer 1

The ptime has no associated timezone information. It does not know whether the content is in UTC or local time. In fact, you could do silly things like:

#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/c_local_time_adjustor.hpp>
#include <iostream>

int main()
{
    using namespace boost::posix_time;

    ptime pt1 = microsec_clock::local_time();
    std::cout << "Local: " << pt1 << std::endl;
    std::cout << "UTC:   " << microsec_clock::universal_time() << std::endl;

    // !!!
    ptime pt2 = boost::date_time::c_local_adjustor<ptime>::utc_to_local(pt1);   
    std::cout << "Oops:  " << pt2 << std::endl;
}

and it will happily create a meaningless time for you.