Long live Qt 4.5!

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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the either Technology Preview License Agreement or the
+** Beta Release License Agreement.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain
+** additional rights. These rights are described in the Nokia Qt LGPL
+** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
+** package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+** If you are unsure which license is appropriate for your use, please
+** contact the sales department at qt-sales@nokia.com.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "dialog.h"
+#include <QFileDialog>
+#include <QBuffer>
+#include <QtCore/QDebug>
+
+/*!
+  \class Dialog
+
+  \brief This class is a simple example of how to use QSharedMemory.
+
+  It is a simple dialog that presents a few buttons. To compile the
+  example, run make in qt/examples/ipc. Then run the executable twice
+  to create two processes running the dialog. In one of the processes,
+  press the button to load an image into a shared memory segment, and
+  then select an image file to load. Once the first process has loaded
+  and displayed the image, in the second process, press the button to
+  read the same image from shared memory. The second process displays
+  the same image loaded from its new loaction in shared memory.
+*/
+
+/*!
+  The class contains a data member \l {QSharedMemory} {sharedMemory},
+  which is initialized with the key "QSharedMemoryExample" to force
+  all instances of Dialog to access the same shared memory segment.
+  The constructor also connects the clicked() signal from each of the
+  three dialog buttons to the slot function appropriate for handling
+  each button.
+*/
+//! [0]
+Dialog::Dialog(QWidget *parent)
+  : QDialog(parent), sharedMemory("QSharedMemoryExample")
+{
+    ui.setupUi(this);
+    connect(ui.loadFromFileButton, SIGNAL(clicked()), SLOT(loadFromFile()));
+    connect(ui.loadFromSharedMemoryButton,
+	    SIGNAL(clicked()),
+	    SLOT(loadFromMemory()));
+    setWindowTitle(tr("SharedMemory Example"));
+}
+//! [0]
+
+/*!
+  This slot function is called when the \tt {Load Image From File...}
+  button is pressed on the firs Dialog process. First, it tests
+  whether the process is already connected to a shared memory segment
+  and, if so, detaches from that segment. This ensures that we always
+  start the example from the beginning if we run it multiple times
+  with the same two Dialog processes. After detaching from an existing
+  shared memory segment, the user is prompted to select an image file.
+  The selected file is loaded into a QImage. The QImage is displayed
+  in the Dialog and streamed into a QBuffer with a QDataStream.
+
+  Next, it gets a new shared memory segment from the system big enough
+  to hold the image data in the QBuffer, and it locks the segment to
+  prevent the second Dialog process from accessing it. Then it copies
+  the image from the QBuffer into the shared memory segment. Finally,
+  it unlocks the shared memory segment so the second Dialog process
+  can access it.
+
+  After this function runs, the user is expected to press the \tt
+  {Load Image from Shared Memory} button on the second Dialog process.
+
+  \sa loadFromMemory()
+ */
+//! [1]
+void Dialog::loadFromFile()
+{
+    if (sharedMemory.isAttached())
+        detach();
+
+    ui.label->setText(tr("Select an image file"));
+    QString fileName = QFileDialog::getOpenFileName(0, QString(), QString(),
+                                        tr("Images (*.png *.xpm *.jpg)"));
+    QImage image;
+    if (!image.load(fileName)) {
+        ui.label->setText(tr("Selected file is not an image, please select another."));
+        return;
+    }
+    ui.label->setPixmap(QPixmap::fromImage(image));
+//! [1] //! [2]
+
+    // load into shared memory
+    QBuffer buffer;
+    buffer.open(QBuffer::ReadWrite);
+    QDataStream out(&buffer);
+    out << image;
+    int size = buffer.size();
+
+    if (!sharedMemory.create(size)) {
+        ui.label->setText(tr("Unable to create shared memory segment."));
+        return;
+    }
+    sharedMemory.lock();
+    char *to = (char*)sharedMemory.data();
+    const char *from = buffer.data().data();
+    memcpy(to, from, qMin(sharedMemory.size(), size));
+    sharedMemory.unlock();
+}
+//! [2]
+
+/*!
+  This slot function is called in the second Dialog process, when the
+  user presses the \tt {Load Image from Shared Memory} button. First,
+  it attaches the process to the shared memory segment created by the
+  first Dialog process. Then it locks the segment for exclusive
+  access, copies the image data from the segment into a QBuffer, and
+  streams the QBuffer into a QImage. Then it unlocks the shared memory
+  segment, detaches from it, and finally displays the QImage in the
+  Dialog.
+
+  \sa loadFromFile()
+ */
+//! [3]
+void Dialog::loadFromMemory()
+{
+    if (!sharedMemory.attach()) {
+        ui.label->setText(tr("Unable to attach to shared memory segment.\n" \
+			     "Load an image first."));
+        return;
+    }
+
+    QBuffer buffer;
+    QDataStream in(&buffer);
+    QImage image;
+
+    sharedMemory.lock();
+    buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
+    buffer.open(QBuffer::ReadOnly);
+    in >> image;
+    sharedMemory.unlock();
+
+    sharedMemory.detach();
+    ui.label->setPixmap(QPixmap::fromImage(image));
+}
+//! [3]
+
+/*!
+  This private function is called by the destructor to detach the
+  process from its shared memory segment. When the last process
+  detaches from a shared memory segment, the system releases the
+  shared memory.
+ */
+void Dialog::detach()
+{
+    if (!sharedMemory.detach()) 
+        ui.label->setText(tr("Unable to detach from shared memory."));
+}
+