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<h1 class="title">dialog.cpp Example File</h1>
<span class="subtitle">ipc/sharedmemory/dialog.cpp</span>
<!-- $$$ipc/sharedmemory/dialog.cpp-description -->
<div class="descr"> <a name="details"></a>
<pre class="cpp">
<span class="comment">/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
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** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
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<span class="preprocessor">#include "dialog.h"</span>
<span class="preprocessor">#include <QFileDialog></span>
<span class="preprocessor">#include <QBuffer></span>
<span class="preprocessor">#include <QtCore/QDebug></span>
<span class="comment">/*!
\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.
*/</span>
<span class="comment">/*!
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.
*/</span>
Dialog<span class="operator">::</span>Dialog(<span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span>parent)
: <span class="type"><a href="../qtwidgets/qdialog.html">QDialog</a></span>(parent)<span class="operator">,</span> sharedMemory(<span class="string">"QSharedMemoryExample"</span>)
{
ui<span class="operator">.</span>setupUi(<span class="keyword">this</span>);
connect(ui<span class="operator">.</span>loadFromFileButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> SLOT(loadFromFile()));
connect(ui<span class="operator">.</span>loadFromSharedMemoryButton<span class="operator">,</span>
SIGNAL(clicked())<span class="operator">,</span>
SLOT(loadFromMemory()));
setWindowTitle(tr(<span class="string">"SharedMemory Example"</span>));
}
<span class="comment">/*!
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()
*/</span>
<span class="type">void</span> Dialog<span class="operator">::</span>loadFromFile()
{
<span class="keyword">if</span> (sharedMemory<span class="operator">.</span>isAttached())
detach();
ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Select an image file"</span>));
<span class="type"><a href="qstring.html">QString</a></span> fileName <span class="operator">=</span> <span class="type"><a href="../qtwidgets/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>
tr(<span class="string">"Images (*.png *.xpm *.jpg)"</span>));
<span class="type"><a href="../qtgui/qimage.html">QImage</a></span> image;
<span class="keyword">if</span> (<span class="operator">!</span>image<span class="operator">.</span>load(fileName)) {
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>));
<span class="keyword">return</span>;
}
ui<span class="operator">.</span>label<span class="operator">-</span><span class="operator">></span>setPixmap(<span class="type"><a href="../qtgui/qpixmap.html">QPixmap</a></span><span class="operator">::</span>fromImage(image));
<span class="comment">// load into shared memory</span>
<span class="type"><a href="qbuffer.html">QBuffer</a></span> buffer;
buffer<span class="operator">.</span>open(<span class="type"><a href="qbuffer.html">QBuffer</a></span><span class="operator">::</span>ReadWrite);
<span class="type"><a href="qdatastream.html">QDataStream</a></span> out(<span class="operator">&</span>buffer);
out <span class="operator"><</span><span class="operator"><</span> image;
<span class="type">int</span> size <span class="operator">=</span> buffer<span class="operator">.</span>size();
<span class="keyword">if</span> (<span class="operator">!</span>sharedMemory<span class="operator">.</span>create(size)) {
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>));
<span class="keyword">return</span>;
}
sharedMemory<span class="operator">.</span>lock();
<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();
<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();
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));
sharedMemory<span class="operator">.</span>unlock();
}
<span class="comment">/*!
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()
*/</span>
<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>));
<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="../qtgui/qimage.html">QImage</a></span> image;
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());
buffer<span class="operator">.</span>open(<span class="type"><a href="qbuffer.html">QBuffer</a></span><span class="operator">::</span>ReadOnly);
in <span class="operator">></span><span class="operator">></span> image;
sharedMemory<span class="operator">.</span>unlock();
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="../qtgui/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
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>
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<!-- @@@ipc/sharedmemory/dialog.cpp -->
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