Improve QString doc when using non-spaced numbered place marker

Currently when a developer uses a string like
QString("%1%3%2").arg(x).arg(y).arg(z) he can be bitten by the
sequential replacement done by QString. Adding an example with a little
explanation should help future Qt user avoid generating buggy strings.

Task-number: QTBUG-44044
Change-Id: I81e20af8d9fb2a07e12ec61dcd5bb4544d863777
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index c933e261cc..bbb5647eea 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -7206,6 +7206,25 @@ QString QString::arg(const QString &a, int fieldWidth, QChar fillChar) const
   difference if \a a1 contains e.g. \c{%1}:
 
   \snippet qstring/main.cpp 13
+
+  A similar problem occurs when the numbered place markers are not
+  white space separated:
+
+  \snippet qstring/main.cpp 12
+  \snippet qstring/main.cpp 97
+
+  Let's look at the substitutions:
+  \list
+  \li First, \c Hello replaces \c {%1} so the string becomes \c {"Hello%3%2"}.
+  \li Then, \c 20 replaces \c {%2} so the string becomes \c {"Hello%320"}.
+  \li Since the maximum numbered place marker value is 99, \c 50 replaces \c {%32}.
+  \endlist
+  Thus the string finally becomes \c {"Hello500"}.
+
+  In such cases, the following yields the expected results:
+
+  \snippet qstring/main.cpp 12
+  \snippet qstring/main.cpp 98
 */
 
 /*!