QString: add resize(int, QChar)

This will be used in QTextStream to speed up padding processing.

[ChangeLog][QtCore][QString] Added resize(int, QChar) overload.

Change-Id: Id51f8cdacb167310157100b05cacf20e9a5d2716
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/doc/snippets/qstring/main.cpp

@@ -625,7 +625,7 @@ void Widget::resizeFunction()
 
     //! [46]
     QString t = "Hello";
-    t += QString(10, 'X');
+    r.resize(t.size() + 10, 'X');
     // t == "HelloXXXXXXXXXX"
     //! [46]
 

src/corelib/tools/qstring.cpp

@@ -1652,9 +1652,7 @@ QString::QString(QChar ch)
     \snippet qstring/main.cpp 45
 
     If you want to append a certain number of identical characters to
-    the string, use \l operator+=() as follows rather than resize():
-
-    \snippet qstring/main.cpp 46
+    the string, use the \l {QString::}{resize(int, QChar)} overload.
 
     If you want to expand the string so that it reaches a certain
     width and fill the new positions with a particular character, use
@@ -1694,6 +1692,25 @@ void QString::resize(int size)
     }
 }
 
+/*!
+    \overload
+    \since 5.7
+
+    Unlike \l {QString::}{resize(int)}, this overload
+    initializes the new characters to \a fillChar:
+
+    \snippet qstring/main.cpp 46
+*/
+
+void QString::resize(int size, QChar fillChar)
+{
+    const int oldSize = length();
+    resize(size);
+    const int difference = length() - oldSize;
+    if (difference > 0)
+        std::fill_n(d->begin() + oldSize, difference, fillChar.unicode());
+}
+
 /*! \fn int QString::capacity() const
 
     Returns the maximum number of characters that can be stored in

src/corelib/tools/qstring.h

@@ -233,6 +233,7 @@ public:
     inline int length() const;
     inline bool isEmpty() const;
     void resize(int size);
+    void resize(int size, QChar fillChar);
 
     QString &fill(QChar c, int size = -1);
     void truncate(int pos);

tests/auto/corelib/tools/qstring/tst_qstring.cpp

@@ -556,6 +556,7 @@ private slots:
     void nanAndInf();
     void compare_data();
     void compare();
+    void resize();
     void resizeAfterFromRawData();
     void resizeAfterReserve();
     void resizeWithNegative() const;
@@ -6013,6 +6014,22 @@ void tst_QString::compare()
     }
 }
 
+void tst_QString::resize()
+{
+    QString s = QLatin1String("hello world");
+
+    s.resize(5);
+    QCOMPARE(s, QLatin1String("hello"));
+    s.resize(8);
+    QCOMPARE(s.size(), 8);
+    QVERIFY(s.startsWith(QLatin1String("hello")));
+
+    s.resize(10, QLatin1Char('n'));
+    QCOMPARE(s.size(), 10);
+    QVERIFY(s.startsWith(QLatin1String("hello")));
+    QCOMPARE(s.right(2), QLatin1String("nn"));
+}
+
 void tst_QString::resizeAfterFromRawData()
 {
     QString buffer("hello world");