Clarify how two digit years are parsed by QDateTime::fromString().

It's currently not obvious that two digit years will always be in the
20th century (1900's).

Task-number: QTBUG-28797
Change-Id: I7dee9a46e0cb803a8f097debc5443d1789c2f16c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>

2 files changed, 27 insertions, 1 deletions

diff --git a/src/corelib/doc/snippets/code/src_corelib_tools_qdatetime.cpp b/src/corelib/doc/snippets/code/src_corelib_tools_qdatetime.cpp
index a2b128800e..d57c1314a8 100644
--- a/src/corelib/doc/snippets/code/src_corelib_tools_qdatetime.cpp
+++ b/src/corelib/doc/snippets/code/src_corelib_tools_qdatetime.cpp
@@ -143,6 +143,8 @@ QDateTime dateTime = QDateTime::fromString("130", "Mm"); // invalid
 //! [14]
 QDateTime dateTime = QDateTime::fromString("1.30.1", "M.d.s");
 // dateTime is January 30 in 1900 at 00:00:01.
+dateTime = QDateTime::fromString("12", "yy");
+// dateTime is January 1 in 1912 at 00:00:00.
 //! [14]
 
 //! [15]
@@ -191,4 +193,16 @@ UTC.setTimeSpec(Qt::UTC);
 qDebug() << "UTC time is:" << UTC;
 
 qDebug() << "There are" << local.secsTo(UTC) << "seconds difference between the datetimes.";
-//! [19]
\ No newline at end of file
+//! [19]
+
+//! [20]
+QString string = "Monday, 23 April 12 22:51:41";
+QString format = "dddd, d MMMM yy hh:mm:ss";
+QDateTime invalid = QDateTime::fromString(string, format);
+//! [20]
+
+//! [21]
+QString string = "Tuesday, 23 April 12 22:51:41";
+QString format = "dddd, d MMMM yy hh:mm:ss";
+QDateTime valid = QDateTime::fromString(string, format);
+//! [21]
diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index 9ac4c1a87f..9949aeb7a1 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -3533,6 +3533,18 @@ QDateTime QDateTime::fromString(const QString& s, Qt::DateFormat f)
     This could have meant 1 January 00:30.00 but the M will grab
     two digits.
 
+    Incorrectly specified fields of the \a string will cause an invalid
+    QDateTime to be returned. For example, consider the following code,
+    where the two digit year 12 is read as 1912 (see the table below for all
+    field defaults); the resulting datetime is invalid because 23 April 1912
+    was a Tuesday, not a Monday:
+
+    \snippet code/src_corelib_tools_qdatetime.cpp 20
+
+    The correct code is:
+
+    \snippet code/src_corelib_tools_qdatetime.cpp 21
+
     For any field that is not represented in the format, the following
     defaults are used: