How to round to the next hour given boost :: posix_time :: ptime

Question

Considering

boost::posix_time::ptime aTime( time_from_string("2012-01-01 11:15:00"));

My function will return 2012-01-01 12:00:00

or given boundary case:

boost::posix_time::ptime boundaryTime( time_from_string("2012-01-01 23:45:00"));

My function will return

2012-01-02 00:00:00

Answer 1

Here is an example. I suggested that fractional seconds should be ignored. I also suggested that if the initial time was already exactly one hour, then it does not need to be increased until the next hour.

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

namespace bpt = boost::posix_time;

bpt::ptime roundedToNextHour(const bpt::ptime& time)
{
    // Get time-of-day portion of the time, ignoring fractional seconds
    bpt::time_duration tod = bpt::seconds(time.time_of_day().total_seconds());

    // Round time-of-day down to start of the hour
    bpt::time_duration roundedDownTod = bpt::hours(tod.hours());

    // Construct the result with the same date, but with the rounded-down
    // time-of-day.
    bpt::ptime result(time.date(), roundedDownTod);

    // If the original time was not already on the hour, add one-hour to the
    // result. Boost knows how to handle the case where time overflows to the
    // next day.
    if (tod != roundedDownTod)
        result += bpt::hours(1);

    return result;
}

int main()
{
    bpt::ptime aTime( bpt::time_from_string("2012-01-01 11:15:00"));
    bpt::ptime boundaryTime( bpt::time_from_string("2012-01-01 23:45:00"));
    bpt::ptime onTheHour( bpt::time_from_string("2012-01-01 23:00:00"));

    std::cout << roundedToNextHour(aTime) << "\n";
    std::cout << roundedToNextHour(boundaryTime) << "\n";
    std::cout << roundedToNextHour(onTheHour) << "\n";
}

Conclusion:

2012-Jan-01 12:00:00
2012-Jan-02 00:00:00
2012-Jan-01 23:00:00

I hope this example helped you learn how Boost Posix Time works.