Clarify how days are counted in QDateTime::daysTo documentation.

Mention that the days are counted as the amount of times midnight is
reached between the start and end date.

Task-number: QTBUG-26780
Change-Id: I22ff6c56b748ac968d6991e0be3e10905c0634bd
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/doc/snippets/code/src_corelib_tools_qdatetime.cpp

@@ -144,3 +144,16 @@ QDateTime dateTime = QDateTime::fromString("130", "Mm"); // invalid
 QDateTime dateTime = QDateTime::fromString("1.30.1", "M.d.s");
 // dateTime is January 30 in 1900 at 00:00:01.
 //! [14]
+
+//! [15]
+QDateTime startDate(QDate(2012, 7, 6), QTime(8, 30, 0));
+QDateTime endDate(QDate(2012, 7, 7), QTime(16, 30, 0));
+qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);
+
+startDate = QDateTime(QDate(2012, 7, 6), QTime(23, 55, 0));
+endDate = QDateTime(QDate(2012, 7, 7), QTime(0, 5, 0));
+qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);
+
+qSwap(startDate, endDate); // Make endDate before startDate.
+qDebug() << "Days from startDate to endDate: " << startDate.daysTo(endDate);
+//! [15]

src/corelib/tools/qdatetime.cpp

@@ -2765,9 +2765,17 @@ QDateTime QDateTime::addMSecs(qint64 msecs) const
 
 /*!
     Returns the number of days from this datetime to the \a other
-    datetime. If the \a other datetime is earlier than this datetime,
+    datetime. The number of days is counted as the number of times
+    midnight is reached between this datetime to the \a other
+    datetime. This means that a 10 minute difference from 23:55 to
+    0:05 the next day counts as one day.
+
+    If the \a other datetime is earlier than this datetime,
     the value returned is negative.
 
+    Example:
+    \snippet code/src_corelib_tools_qdatetime.cpp 15
+
     \sa addDays(), secsTo(), msecsTo()
 */