Qt - 获取两个日期时间对象之间的时间跨度

Question

I have two datetime objects, say, "2013-06-13 11:00:45", "2013-06-14 09:03:23".

How can I get the time span between these two datetimes(in the form of "X days, X hours, X minutes, X seconds")?

Answer 1

Currently, you must use QDateTime::secsTo and then do the math to figure out the days, hours, minutes and seconds.

However, there are plans to add a QTimeSpan class to Qt:

https://qt.gitorious.org/qt/qt/merge_requests/1014

It isn't clear when this will get added to Qt; the merge request is almost 2 years old already. However, you can grab the code from the above merge request and compile it into your project if you'd like.

Answer 2

QTime may help to format the part of the result of QDateTime::secsTo method ( mentioned by @RA ) that is less than a day eg, t.toString("hh:mm:ss.zzz") or:

#include <QString>
#include <QTime>

/// seconds as "X days, X hours, X minutes, X seconds" string
QString secondsToString(qint64 seconds)
{
  const qint64 DAY = 86400;
  qint64 days = seconds / DAY;
  QTime t = QTime(0,0).addSecs(seconds % DAY);
  return QString("%1 days, %2 hours, %3 minutes, %4 seconds")
    .arg(days).arg(t.hour()).arg(t.minute()).arg(t.second());
}

Example:

#include <QDateTime>
#include <QDebug>   

int main()
{
  QString format = "yyyy-MM-dd HH:mm:ss";
  QDateTime a = QDateTime::fromString("2013-06-13 11:00:45", format);
  QDateTime b = QDateTime::fromString("2013-06-14 09:03:23", format);
  qDebug() << secondsToString(a.secsTo(b));
}

Output:

"0 days, 22 hours, 2 minutes, 38 seconds"

By default, the dates use your local timezone. QDateTime::secsTo() converts the dates to "seconds since epoch" before finding the difference ie, if there is a DST transition between the dates or the UTC offset has changes for any other reason then it is taken into account (if the corresponding C mktime() supports it on a given platform). POSIX time does not count leap seconds (you could use a "right" timezone, to count leaps seconds).