QRegularExpressionMatch: add a way to know if a capturing group captured

Relying on the fact that a given capturing group captured a null string
doesn't allow users to distinguish whether a capturing group did not
capture anything, or captured a null substring (say, from a null subject
string).

Perl allows for the distinction: the entries in the @- and @+ arrays are
set to values in case there is a capture, but they're undef otherwise.

PCRE2 gives us the information already in the results "ovector", but
it was simply not exposed to QREM users. So, expose it.

[ChangeLog][QtCore][QRegularExpressionMatch] Added the hasCaptured()
family of functions to know if a given capturing group has captured
something.

Change-Id: Ic1320933d4554e2e313c0a680be1b1b9dd95af0b
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/corelib/doc/snippets/code/src_corelib_text_qregularexpression.cpp b/src/corelib/doc/snippets/code/src_corelib_text_qregularexpression.cpp
index 8bf67a9e2d..3bb9727ca6 100644
--- a/src/corelib/doc/snippets/code/src_corelib_text_qregularexpression.cpp
+++ b/src/corelib/doc/snippets/code/src_corelib_text_qregularexpression.cpp
@@ -374,4 +374,16 @@ QRegularExpression re(R"(\d\d \w+)");
 //! [35]
 }
 
+{
+//! [36]
+QRegularExpression re("([a-z]+)|([A-Z]+)");
+QRegularExpressionMatch m = re.match("UPPERCASE");
+if (m.hasMatch()) {
+    qDebug() << m.hasCaptured(0); // true
+    qDebug() << m.hasCaptured(1); // false
+    qDebug() << m.hasCaptured(2); // true
+}
+//! [36]
+}
+
 }