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<h1 class="title">Q3DeepCopy Class Reference</h1>
<!-- $$$Q3DeepCopy-brief -->
<p>The Q3DeepCopy class is a template class which ensures that implicitly shared and explicitly shared classes reference unique data. <a href="#details">More...</a></p>
<!-- @@@Q3DeepCopy -->
<pre class="cpp"> <span class="preprocessor">#include <Q3DeepCopy></span></pre><p><b>This class is part of the Qt 3 support library.</b> It is provided to keep old source code working. We strongly advise against using it in new code. See <a href="porting4.html">Porting to Qt 4</a> for more information.</p>
<p><b>Note:</b> All functions in this class are <a href="threads-reentrancy.html#reentrant">reentrant</a>.</p>
<ul>
<li><a href="q3deepcopy-members.html">List of all members, including inherited members</a></li>
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<a name="public-functions"></a>
<h2>Public Functions</h2>
<table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="q3deepcopy.html#Q3DeepCopy">Q3DeepCopy</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="q3deepcopy.html#Q3DeepCopy-2">Q3DeepCopy</a></b> ( const T & <i>t</i> )</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="q3deepcopy.html#operator-T">operator T</a></b> ()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> Q3DeepCopy<T> & </td><td class="memItemRight bottomAlign"><b><a href="q3deepcopy.html#operator-eq">operator=</a></b> ( const T & <i>t</i> )</td></tr>
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<a name="details"></a>
<!-- $$$Q3DeepCopy-description -->
<div class="descr">
<h2>Detailed Description</h2>
<p>The Q3DeepCopy class is a template class which ensures that implicitly shared and explicitly shared classes reference unique data.</p>
<p>Normally, shared copies reference the same data to optimize memory use and for maximum speed. In the example below, <tt>s1</tt>, <tt>s2</tt>, <tt>s3</tt>, <tt>s4</tt> and <tt>s5</tt> share data.</p>
<pre class="cpp"> <span class="comment">// all 5 strings share the same data</span>
<span class="type"><a href="qstring.html">QString</a></span> s1 <span class="operator">=</span> <span class="string">"abcd"</span>;
<span class="type"><a href="qstring.html">QString</a></span> s2 <span class="operator">=</span> s1;
<span class="type"><a href="qstring.html">QString</a></span> s3 <span class="operator">=</span> s2;
<span class="type"><a href="qstring.html">QString</a></span> s4 <span class="operator">=</span> s3;
<span class="type"><a href="qstring.html">QString</a></span> s5 <span class="operator">=</span> s2;</pre>
<p>Q3DeepCopy can be used several ways to ensure that an object references unique, unshared data. In the example below, <tt>s1</tt>, <tt>s2</tt> and <tt>s5</tt> share data, while neither <tt>s3</tt> nor <tt>s4</tt> share data.</p>
<pre class="cpp"> <span class="comment">// s1, s2 and s5 share the same data, neither s3 nor s4 are shared</span>
<span class="type"><a href="qstring.html">QString</a></span> s1 <span class="operator">=</span> <span class="string">"abcd"</span>;
<span class="type"><a href="qstring.html">QString</a></span> s2 <span class="operator">=</span> s1;
<span class="type">Q3DeepCopy</span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> s3 <span class="operator">=</span> s2; <span class="comment">// s3 is a deep copy of s2</span>
<span class="type"><a href="qstring.html">QString</a></span> s4 <span class="operator">=</span> s3; <span class="comment">// s4 is a deep copy of s3</span>
<span class="type"><a href="qstring.html">QString</a></span> s5 <span class="operator">=</span> s2;</pre>
<p>In the example below, <tt>s1</tt>, <tt>s2</tt> and <tt>s5</tt> share data, and <tt>s3</tt> and <tt>s4</tt> share data.</p>
<pre class="cpp"> <span class="comment">// s1, s2 and s5 share the same data, s3 and s4 share the same data</span>
<span class="type"><a href="qstring.html">QString</a></span> s1 <span class="operator">=</span> <span class="string">"abcd"</span>;
<span class="type"><a href="qstring.html">QString</a></span> s2 <span class="operator">=</span> s1;
<span class="type"><a href="qstring.html">QString</a></span> s3 <span class="operator">=</span> <span class="type">Q3DeepCopy</span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span>( s2 ); <span class="comment">// s3 is a deep copy of s2</span>
<span class="type"><a href="qstring.html">QString</a></span> s4 <span class="operator">=</span> s3; <span class="comment">// s4 is a shallow copy of s3</span>
<span class="type"><a href="qstring.html">QString</a></span> s5 <span class="operator">=</span> s2;</pre>
<p>Q3DeepCopy can also provide safety in multithreaded applications that use shared classes. In the example below, the variable <tt>global_string</tt> is used safely since the data contained in <tt>global_string</tt> is always a deep copy. This ensures that all threads get a unique copy of the data, and that any assignments to <tt>global_string</tt> will result in a deep copy.</p>
<pre class="cpp"> <span class="type">Q3DeepCopy</span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> global_string; <span class="comment">// global string data</span>
<span class="type"><a href="qmutex.html">QMutex</a></span> global_mutex; <span class="comment">// mutex to protext global_string</span>
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type">void</span> setGlobalString( <span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>str )
{
global_mutex<span class="operator">.</span>lock();
global_string <span class="operator">=</span> str; <span class="comment">// global_string is a deep copy of str</span>
global_mutex<span class="operator">.</span>unlock();
}
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type">void</span> MyThread<span class="operator">::</span>run()
{
global_mutex<span class="operator">.</span>lock();
<span class="type"><a href="qstring.html">QString</a></span> str <span class="operator">=</span> global_string; <span class="comment">// str is a deep copy of global_string</span>
global_mutex<span class="operator">.</span>unlock();
<span class="comment">// process the string data</span>
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="comment">// update global_string</span>
setGlobalString( str );
}</pre>
<p><b>Warning:</b> It is the application developer's responsibility to protect the object shared across multiple threads.</p>
<p>The examples above use <a href="qstring.html">QString</a>, which is an implicitly shared class. The behavior of Q3DeepCopy is the same when using explicitly shared classes like <a href="qbytearray.html">QByteArray</a>.</p>
<p>Currently, Q3DeepCopy works with the following classes:</p>
<ul>
<li>QMemArray (including subclasses like <a href="qbytearray.html">QByteArray</a> and <a href="porting4.html#qcstring">QCString</a>)</li>
<li><a href="qmap.html">QMap</a></li>
<li><a href="qstring.html">QString</a></li>
<li>QValueList (including subclasses like <a href="qstringlist.html">QStringList</a> and QValueStack)</li>
<li>QValueVector</li>
</ul>
</div>
<p><b>See also </b><a href="threads.html">Thread Support in Qt</a>.</p>
<!-- @@@Q3DeepCopy -->
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$Q3DeepCopy[overload1]$$$Q3DeepCopy -->
<h3 class="fn"><a name="Q3DeepCopy"></a>Q3DeepCopy::<span class="name">Q3DeepCopy</span> ()</h3>
<p>Constructs an empty instance of type <i>T</i>.</p>
<!-- @@@Q3DeepCopy -->
<!-- $$$Q3DeepCopy$$$Q3DeepCopyconstT& -->
<h3 class="fn"><a name="Q3DeepCopy-2"></a>Q3DeepCopy::<span class="name">Q3DeepCopy</span> ( const <span class="type">T</span> & <i>t</i> )</h3>
<p>Constructs a deep copy of <i>t</i>.</p>
<!-- @@@Q3DeepCopy -->
<!-- $$$operator T[overload1]$$$operator T -->
<h3 class="fn"><a name="operator-T"></a>Q3DeepCopy::<span class="name">operator T</span> ()</h3>
<p>Returns a deep copy of the encapsulated data.</p>
<!-- @@@operator T -->
<!-- $$$operator=[overload1]$$$operator=constT& -->
<h3 class="fn"><a name="operator-eq"></a><span class="type">Q3DeepCopy</span><<span class="type">T</span>> & Q3DeepCopy::<span class="name">operator=</span> ( const <span class="type">T</span> & <i>t</i> )</h3>
<p>Assigns a deep copy of <i>t</i>.</p>
<!-- @@@operator= -->
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