Boost.Date_Time

#include <iostream>
 
#include <boost/date_time.hpp>
#include <boost/date_time/gregorian/greg_date.hpp>
#include <boost/date_time/time_zone_base.hpp>
#include <boost/date_time/c_local_time_adjustor.hpp>
 
namespace pt = boost::posix_time;
namespace g = boost::gregorian;
using local_adj = boost::date_time::c_local_adjustor<pt::ptime>;
 
int main()
{
    try
    {
        boost::posix_time::ptime first(g::date(1970, 1, 1));
        auto result1 = local_adj::utc_to_local(first);
        std::cout << "first: " << pt::to_simple_string(result1) << std::endl;
 
        boost::posix_time::ptime second(g::date(1969, 1, 1));
        auto result2 = local_adj::utc_to_local(second);
        std::cout << "second: " << pt::to_simple_string(result2) << std::endl;
 
    }
    catch (const std::exception& e)
    {
        std::cout << "std::exception: " << e.what() << std::endl;
    }
 
    std::cin.get();
}

boost::posix_time::ptime convert(boost::posix_time::ptime time)
{
    const static boost::posix_time::ptime epoch(boost::gregorian::date(1970, 1, 1));
 
    boost::posix_time::ptime result;
    if (time > epoch)
    {
        result = boost::date_time::c_local_adjustor<boost::posix_time::ptime>::utc_to_local(time);
    }
    else
    {
        auto delt = epoch - time + boost::posix_time::hours(24);
        time = time + delt;
        result = boost::date_time::c_local_adjustor<boost::posix_time::ptime>::utc_to_local(time) - delt;
    }
    return result;
}