QDateTime提供了与日期和时间的相关操作方法。

A QDateTime object contains a calendar date and a clock time (a "datetime"). It is a combination of the QDate and QTime classes. It can read the current datetime from the system clock. It provides functions for comparing datetimes and for manipulating a datetime by adding a number of seconds, days, months, or years.

编程示例如下：

#include <QCoreApplication>
#include <QtCore>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    auto dt=QDateTime::currentDateTime();
    qDebug() << dt;
    auto birthday=QDateTime::fromString("19820925","yyyyMMdd");
    qDebug() << birthday;
    qDebug() << birthday.toString();
    qDebug() << birthday.toString("yyyy-MM-dd");
    qDebug() << dt.date();
    qDebug() << dt.time();
    qDebug() << birthday.daysTo(dt);
    return a.exec();
}

参考资料：

http://qt-project.org/doc/qt-5/qdatetime.html