383 lines
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<h1 class="title">dialog.cpp Example File</h1>
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<span class="small-subtitle">ipc/sharedmemory/dialog.cpp</span>
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<!-- $$$ipc/sharedmemory/dialog.cpp-description -->
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<div class="descr"> <a name="details"></a>
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<pre class="cpp"> <span class="comment">/****************************************************************************
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**
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** Copyright (C) 2015 The Qt Company Ltd.
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** Contact: http://www.qt.io/licensing/
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**
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** This file is part of the examples of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:BSD$
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** You may use this file under the terms of the BSD license as follows:
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**
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** "Redistribution and use in source and binary forms, with or without
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** modification, are permitted provided that the following conditions are
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** met:
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** * Redistributions of source code must retain the above copyright
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** notice, this list of conditions and the following disclaimer.
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** * Redistributions in binary form must reproduce the above copyright
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** notice, this list of conditions and the following disclaimer in
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** the documentation and/or other materials provided with the
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** distribution.
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** * Neither the name of The Qt Company Ltd nor the names of its
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** contributors may be used to endorse or promote products derived
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** from this software without specific prior written permission.
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**
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**
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** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/</span>
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<span class="preprocessor">#include "dialog.h"</span>
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<span class="preprocessor">#include <QFileDialog></span>
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<span class="preprocessor">#include <QBuffer></span>
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<span class="preprocessor">#include <QtCore/QDebug></span>
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<span class="comment">/*!
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\class Dialog
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\brief This class is a simple example of how to use QSharedMemory.
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It is a simple dialog that presents a few buttons. To compile the
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example, run make in qt/examples/ipc. Then run the executable twice
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to create two processes running the dialog. In one of the processes,
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press the button to load an image into a shared memory segment, and
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then select an image file to load. Once the first process has loaded
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and displayed the image, in the second process, press the button to
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read the same image from shared memory. The second process displays
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the same image loaded from its new loaction in shared memory.
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*/</span>
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<span class="comment">/*!
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The class contains a data member \l {QSharedMemory} {sharedMemory},
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which is initialized with the key "QSharedMemoryExample" to force
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all instances of Dialog to access the same shared memory segment.
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The constructor also connects the clicked() signal from each of the
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three dialog buttons to the slot function appropriate for handling
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each button.
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*/</span>
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Dialog<span class="operator">::</span>Dialog(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent)
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: <span class="type"><a href="qdialog.html">QDialog</a></span>(parent)<span class="operator">,</span> sharedMemory(<span class="string">"QSharedMemoryExample"</span>)
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{
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ui<span class="operator">.</span>setupUi(<span class="keyword">this</span>);
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connect(ui<span class="operator">.</span>loadFromFileButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> SLOT(loadFromFile()));
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connect(ui<span class="operator">.</span>loadFromSharedMemoryButton<span class="operator">,</span>
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SIGNAL(clicked())<span class="operator">,</span>
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SLOT(loadFromMemory()));
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setWindowTitle(tr(<span class="string">"SharedMemory Example"</span>));
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}
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<span class="comment">/*!
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This slot function is called when the \tt {Load Image From File...}
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button is pressed on the firs Dialog process. First, it tests
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whether the process is already connected to a shared memory segment
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and, if so, detaches from that segment. This ensures that we always
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start the example from the beginning if we run it multiple times
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with the same two Dialog processes. After detaching from an existing
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shared memory segment, the user is prompted to select an image file.
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The selected file is loaded into a QImage. The QImage is displayed
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in the Dialog and streamed into a QBuffer with a QDataStream.
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Next, it gets a new shared memory segment from the system big enough
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to hold the image data in the QBuffer, and it locks the segment to
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prevent the second Dialog process from accessing it. Then it copies
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the image from the QBuffer into the shared memory segment. Finally,
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it unlocks the shared memory segment so the second Dialog process
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can access it.
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After this function runs, the user is expected to press the \tt
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{Load Image from Shared Memory} button on the second Dialog process.
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\sa loadFromMemory()
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*/</span>
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<span class="type">void</span> Dialog<span class="operator">::</span>loadFromFile()
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{
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<span class="keyword">if</span> (sharedMemory<span class="operator">.</span>isAttached())
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detach();
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ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Select an image file"</span>));
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<span class="type"><a href="qstring.html">QString</a></span> fileName <span class="operator">=</span> <span class="type"><a href="qfiledialog.html">QFileDialog</a></span><span class="operator">::</span>getOpenFileName(<span class="number">0</span><span class="operator">,</span> <span class="type"><a href="qstring.html">QString</a></span>()<span class="operator">,</span> <span class="type"><a href="qstring.html">QString</a></span>()<span class="operator">,</span>
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tr(<span class="string">"Images (*.png *.xpm *.jpg)"</span>));
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<span class="type"><a href="qimage.html">QImage</a></span> image;
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<span class="keyword">if</span> (<span class="operator">!</span>image<span class="operator">.</span>load(fileName)) {
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ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Selected file is not an image, please select another."</span>));
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<span class="keyword">return</span>;
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}
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ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setPixmap(<span class="type"><a href="qpixmap.html">QPixmap</a></span><span class="operator">::</span>fromImage(image));
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<span class="comment">// load into shared memory</span>
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<span class="type"><a href="qbuffer.html">QBuffer</a></span> buffer;
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buffer<span class="operator">.</span>open(<span class="type"><a href="qbuffer.html">QBuffer</a></span><span class="operator">::</span>ReadWrite);
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<span class="type"><a href="qdatastream.html">QDataStream</a></span> out(<span class="operator">&</span>buffer);
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out <span class="operator"><</span><span class="operator"><</span> image;
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<span class="type">int</span> size <span class="operator">=</span> buffer<span class="operator">.</span>size();
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<span class="keyword">if</span> (<span class="operator">!</span>sharedMemory<span class="operator">.</span>create(size)) {
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ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Unable to create shared memory segment."</span>));
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<span class="keyword">return</span>;
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}
|
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sharedMemory<span class="operator">.</span>lock();
|
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<span class="type">char</span> <span class="operator">*</span>to <span class="operator">=</span> (<span class="type">char</span><span class="operator">*</span>)sharedMemory<span class="operator">.</span>data();
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<span class="keyword">const</span> <span class="type">char</span> <span class="operator">*</span>from <span class="operator">=</span> buffer<span class="operator">.</span>data()<span class="operator">.</span>data();
|
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memcpy(to<span class="operator">,</span> from<span class="operator">,</span> <a href="qtglobal.html#qMin">qMin</a>(sharedMemory<span class="operator">.</span>size()<span class="operator">,</span> size));
|
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sharedMemory<span class="operator">.</span>unlock();
|
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}
|
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|
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<span class="comment">/*!
|
|
This slot function is called in the second Dialog process, when the
|
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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
|
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streams the QBuffer into a QImage. Then it unlocks the shared memory
|
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segment, detaches from it, and finally displays the QImage in the
|
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Dialog.
|
|
|
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\sa loadFromFile()
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*/</span>
|
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<span class="type">void</span> Dialog<span class="operator">::</span>loadFromMemory()
|
|
{
|
|
<span class="keyword">if</span> (<span class="operator">!</span>sharedMemory<span class="operator">.</span>attach()) {
|
|
ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Unable to attach to shared memory segment.\n"</span> \
|
|
<span class="string">"Load an image first."</span>));
|
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<span class="keyword">return</span>;
|
|
}
|
|
|
|
<span class="type"><a href="qbuffer.html">QBuffer</a></span> buffer;
|
|
<span class="type"><a href="qdatastream.html">QDataStream</a></span> in(<span class="operator">&</span>buffer);
|
|
<span class="type"><a href="qimage.html">QImage</a></span> image;
|
|
|
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sharedMemory<span class="operator">.</span>lock();
|
|
buffer<span class="operator">.</span>setData((<span class="type">char</span><span class="operator">*</span>)sharedMemory<span class="operator">.</span>constData()<span class="operator">,</span> sharedMemory<span class="operator">.</span>size());
|
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buffer<span class="operator">.</span>open(<span class="type"><a href="qbuffer.html">QBuffer</a></span><span class="operator">::</span>ReadOnly);
|
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in <span class="operator">></span><span class="operator">></span> image;
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sharedMemory<span class="operator">.</span>unlock();
|
|
|
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sharedMemory<span class="operator">.</span>detach();
|
|
ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setPixmap(<span class="type"><a href="qpixmap.html">QPixmap</a></span><span class="operator">::</span>fromImage(image));
|
|
}
|
|
|
|
<span class="comment">/*!
|
|
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
|
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shared memory.
|
|
*/</span>
|
|
<span class="type">void</span> Dialog<span class="operator">::</span>detach()
|
|
{
|
|
<span class="keyword">if</span> (<span class="operator">!</span>sharedMemory<span class="operator">.</span>detach())
|
|
ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Unable to detach from shared memory."</span>));
|
|
}</pre>
|
|
</div>
|
|
<!-- @@@ipc/sharedmemory/dialog.cpp -->
|
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</div>
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</div>
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</div>
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<span></span>
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</div>
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</div>
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<div class="footer">
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<p>
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<acronym title="Copyright">©</acronym> 2015 The Qt Company Ltd.
|
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Documentation contributions included herein are the copyrights of
|
|
their respective owners.</p>
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<br />
|
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<p>
|
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The documentation provided herein is licensed under the terms of the
|
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<a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation
|
|
License version 1.3</a> as published by the Free Software Foundation.</p>
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<p>
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