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authorGiuseppe D'Angelo <>2019-12-24 12:29:53 +0100
committerGiuseppe D'Angelo <>2019-12-24 22:28:59 +0100
commitd24a1d4323e73400ef4ecca99e03ff0f41c60389 (patch)
parentfa39d3404349dd52f88a8e0e0942399a68dcf200 (diff)
QRegularExpression: improve docs about porting from QRegExp
Change-Id: Ie5d737188977b0e4dc1070c2d7329d0ecb6a9308 Reviewed-by: David Faure <>
1 files changed, 32 insertions, 0 deletions
diff --git a/src/corelib/text/qregularexpression.cpp b/src/corelib/text/qregularexpression.cpp
index 8d2187eb28..a02d471134 100644
--- a/src/corelib/text/qregularexpression.cpp
+++ b/src/corelib/text/qregularexpression.cpp
@@ -443,6 +443,38 @@ QT_BEGIN_NAMESPACE
Other differences are outlined below.
+ \section2 Different pattern syntax
+ Porting a regular expression from QRegExp to QRegularExpression may require
+ changes to the pattern itself.
+ In certain scenarios, QRegExp was too lenient and accepted patterns that
+ are simply invalid when using QRegularExpression. These are somehow easy
+ to detect, because the QRegularExpression objects built with these patterns
+ are not valid (cf. isValid()).
+ In other cases, a pattern ported from QRegExp to QRegularExpression may
+ silently change semantics. Therefore, it is necessary to review the
+ patterns used. The most notable cases of silent incompatibility are:
+ \list
+ \li Curly braces are needed in order to use a hexadecimal escape like
+ \c{\xHHHH} with more than 2 digits. A pattern like \c{\x2022} neeeds to
+ be ported to \c{\x{2022}}, or it will match a space (\c{0x20}) followed
+ by the string \c{"22"}. In general, it is highly recommended to always use
+ curly braces with the \c{\\x} escape, no matter the amount of digits
+ specified.
+ \li A 0-to-n quantification like \c{{,n}} needs to be ported to c{{0,n}} to
+ preserve semantics. Otherwise, a pattern such as \c{\d{,3}} would
+ actually match a digit followed by the exact string \c{"{,3}"}.
+ \li QRegExp by default does Unicode-aware matching, while
+ QRegularExpression requires a separate option; see below for more details.
+ \endlist
\section2 Porting from QRegExp::exactMatch()
QRegExp::exactMatch() in Qt 4 served two purposes: it exactly matched