Add conversion functions for C++11 u16string and u32string

The patch adds convenience functions for working on C++11's new char
width specific unicode strings u16string and u32string.

[ChangeLog][QtCore][QString] Added methods for convenient conversion
to and from std::u16string and std::u32string.

Change-Id: I67c082e4755c592d61daaaaa70c8867ef0b23dcb
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/tools/qstring.cpp

@@ -1356,7 +1356,7 @@ const QString::Null QString::null = { };
     windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix
     systems).
 
-    \sa fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), fromUcs4()
+    \sa fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), fromUcs4(), fromStdU16String(), fromStdU32String()
 */
 
 /*! \fn QString QString::fromWCharArray(const wchar_t *string, int size)
@@ -1381,7 +1381,7 @@ const QString::Null QString::null = { };
     This method is mostly useful to pass a QString to a function
     that accepts a std::wstring object.
 
-    \sa utf16(), toLatin1(), toUtf8(), toLocal8Bit()
+    \sa utf16(), toLatin1(), toUtf8(), toLocal8Bit(), toStdU16String(), toStdU32String()
 */
 
 int QString::toUcs4_helper(const ushort *uc, int length, uint *out)
@@ -4632,7 +4632,7 @@ QString QString::fromUtf8_helper(const char *str, int size)
 
     QString makes a deep copy of the Unicode data.
 
-    \sa utf16(), setUtf16()
+    \sa utf16(), setUtf16(), fromStdU16String()
 */
 QString QString::fromUtf16(const ushort *unicode, int size)
 {
@@ -4656,7 +4656,7 @@ QString QString::fromUtf16(const ushort *unicode, int size)
     If \a size is -1 (default), \a unicode must be terminated
     with a 0.
 
-    \sa toUcs4(), fromUtf16(), utf16(), setUtf16(), fromWCharArray()
+    \sa toUcs4(), fromUtf16(), utf16(), setUtf16(), fromWCharArray(), fromStdU32String()
 */
 QString QString::fromUcs4(const uint *unicode, int size)
 {
@@ -7887,6 +7887,46 @@ QString &QString::setRawData(const QChar *unicode, int size)
     return *this;
 }
 
+/*! \fn QString QString::fromStdU16String(const std::u16string &str)
+    \since 5.5
+
+    Returns a copy of the \a str string. The given string is assumed
+    to be encoded in UTF-16.
+
+    \sa fromUtf16(), fromStdWString(), fromStdU32String()
+*/
+
+/*!
+    \fn std::u16string QString::toStdU16String() const
+    \since 5.5
+
+    Returns a std::u16string object with the data contained in this
+    QString. The Unicode data is the same as returned by the utf16()
+    method.
+
+    \sa utf16(), toStdWString(), toStdU32String()
+*/
+
+/*! \fn QString QString::fromStdU32String(const std::u32string &str)
+    \since 5.5
+
+    Returns a copy of the \a str string. The given string is assumed
+    to be encoded in UCS-4.
+
+    \sa fromUcs4(), fromStdWString(), fromStdU16String()
+*/
+
+/*!
+    \fn std::u32string QString::toStdU32String() const
+    \since 5.5
+
+    Returns a std::u32string object with the data contained in this
+    QString. The Unicode data is the same as returned by the toUcs4()
+    method.
+
+    \sa toUcs4(), toStdWString(), toStdU16String()
+*/
+
 /*! \class QLatin1String
     \inmodule QtCore
     \brief The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal.

src/corelib/tools/qstring.h

@@ -733,6 +733,13 @@ public:
     static inline QString fromStdWString(const std::wstring &s);
     inline std::wstring toStdWString() const;
 
+#if defined(Q_COMPILER_UNICODE_STRINGS) || defined(Q_QDOC)
+    static inline QString fromStdU16String(const std::u16string &s);
+    inline std::u16string toStdU16String() const;
+    static inline QString fromStdU32String(const std::u32string &s);
+    inline std::u32string toStdU32String() const;
+#endif
+
 #if defined(Q_OS_MAC) || defined(Q_QDOC)
     static QString fromCFString(CFStringRef string);
     CFStringRef toCFString() const Q_DECL_CF_RETURNS_RETAINED;
@@ -1294,6 +1301,25 @@ inline std::wstring QString::toStdWString() const
 inline QString QString::fromStdWString(const std::wstring &s)
 { return fromWCharArray(s.data(), int(s.size())); }
 
+#if defined(Q_COMPILER_UNICODE_STRINGS)
+inline QString QString::fromStdU16String(const std::u16string &s)
+{ return fromUtf16(s.data(), int(s.size())); }
+
+inline std::u16string QString::toStdU16String() const
+{ return std::u16string(reinterpret_cast<const char16_t*>(utf16()), length()); }
+
+inline QString QString::fromStdU32String(const std::u32string &s)
+{ return fromUcs4(s.data(), int(s.size())); }
+
+inline std::u32string QString::toStdU32String() const
+{
+    std::u32string u32str(length(), char32_t(0));
+    int len = toUcs4_helper(d->data(), length(), reinterpret_cast<uint*>(&u32str[0]));
+    u32str.resize(len);
+    return u32str;
+}
+#endif
+
 #if !defined(QT_NO_DATASTREAM) || (defined(QT_BOOTSTRAPPED) && !defined(QT_BUILD_QMAKE))
 Q_CORE_EXPORT QDataStream &operator<<(QDataStream &, const QString &);
 Q_CORE_EXPORT QDataStream &operator>>(QDataStream &, QString &);

tests/auto/corelib/tools/qstring/qstring.pro

@@ -4,6 +4,7 @@ QT = core testlib
 SOURCES = tst_qstring.cpp
 DEFINES += QT_NO_CAST_TO_ASCII
 contains(QT_CONFIG,icu):DEFINES += QT_USE_ICU
+contains(QT_CONFIG,c++11): CONFIG += c++11
 DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
 
 mac {

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

@@ -59,6 +59,7 @@
 #include <locale.h>
 #include <qhash.h>
 
+#include <string>
 
 #define CREATE_REF(string)                                              \
     const QString padded = QString::fromLatin1(" %1 ").arg(string);     \
@@ -263,6 +264,7 @@ private slots:
     void assignQLatin1String();
     void isRightToLeft_data();
     void isRightToLeft();
+    void unicodeStrings();
 };
 
 template <class T> const T &verifyZeroTermination(const T &t) { return t; }
@@ -5222,6 +5224,27 @@ void tst_QString::fromUtf16_char16()
 #endif
 }
 
+void tst_QString::unicodeStrings()
+{
+#ifdef Q_COMPILER_UNICODE_STRINGS
+    QString s1, s2;
+    static const std::u16string u16str1(u"Hello Unicode World");
+    static const std::u32string u32str1(U"Hello Unicode World");
+    s1 = QString::fromStdU16String(u16str1);
+    s2 = QString::fromStdU32String(u32str1);
+    QCOMPARE(s1, QString("Hello Unicode World"));
+    QCOMPARE(s1, s2);
+
+    QCOMPARE(s2.toStdU16String(), u16str1);
+    QCOMPARE(s1.toStdU32String(), u32str1);
+
+    s1 = QString::fromStdU32String(std::u32string(U"\u221212\U000020AC\U00010000"));
+    QCOMPARE(s1, QString::fromUtf8("\342\210\222" "12" "\342\202\254" "\360\220\200\200"));
+#else
+    QSKIP("Compiler does not support C++11 unicode strings");
+#endif
+}
+
 void tst_QString::latin1String()
 {
     QString s("Hello");