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<td align="right" valign="top" width="230"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></td></tr></table><h1 align="center">Q3DeepCopy Class Reference</h1>

<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>

<pre>#include <Q3DeepCopy></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 the <a href="porting4.html">Porting Guide</a> for more information.</p>

<p>Part of the <a href="qt3support.html">Qt3Support</a> module.</p>

<p><b>Note:</b> All the functions in this class are <a href="threads.html#reentrant">reentrant</a>.</p>

<ul>

<li><a href="q3deepcopy-members.html">List of all members, including inherited members</a></li>

</ul>

<h3>Public Functions</h3>

<ul>

<li><div class="fn"/><b><a href="q3deepcopy.html#Q3DeepCopy">Q3DeepCopy</a></b> ()</li>

<li><div class="fn"/><b><a href="q3deepcopy.html#Q3DeepCopy-2">Q3DeepCopy</a></b> ( const T & <i>t</i> )</li>

<li><div class="fn"/><b><a href="q3deepcopy.html#operator-T">operator T</a></b> ()</li>

<li><div class="fn"/>Q3DeepCopy<T> & <b><a href="q3deepcopy.html#operator-eq">operator=</a></b> ( const T & <i>t</i> )</li>

</ul>

<hr />

<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>  // all 5 strings share the same data

QString s1 = "abcd";

QString s2 = s1;

QString s3 = s2;

QString s4 = s3;

QString s5 = 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>  // s1, s2 and s5 share the same data, neither s3 nor s4 are shared

QString s1 = "abcd";

QString s2 = s1;

Q3DeepCopy<QString> s3 = s2; // s3 is a deep copy of s2

QString s4 = s3; // s4 is a deep copy of s3

QString s5 = 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>  // s1, s2 and s5 share the same data, s3 and s4 share the same data

QString s1 = "abcd";

QString s2 = s1;

QString s3 = Q3DeepCopy<QString>( s2 ); // s3 is a deep copy of s2

QString s4 = s3; // s4 is a shallow copy of s3

QString s5 = 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>  Q3DeepCopy<QString> global_string; // global string data

QMutex global_mutex; // mutex to protext global_string

...

void setGlobalString( const QString &str )

{

global_mutex.lock();

global_string = str; // global_string is a deep copy of str

global_mutex.unlock();

}

...

void MyThread::run()

{

global_mutex.lock();

QString str = global_string; // str is a deep copy of global_string

global_mutex.unlock();

// process the string data

...

// update global_string

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="qstring.html">QString</a></li>

<li>QValueList (including subclasses like <a href="qstringlist.html">QStringList</a> and QValueStack)</li>

<li>QValueVector</li>

</ul>

<p>See also <a href="threads.html">Thread Support in Qt</a>.</p>

<hr />

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<h2>Member Function Documentation</h2>

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<h3 class="fn"><a name="Q3DeepCopy"></a>Q3DeepCopy::Q3DeepCopy ()</h3>

102

<p>Constructs an empty instance of type <i>T</i>.</p>

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<h3 class="fn"><a name="Q3DeepCopy-2"></a>Q3DeepCopy::Q3DeepCopy ( const T & <i>t</i> )</h3>

104

<p>Constructs a deep copy of <i>t</i>.</p>

105

<h3 class="fn"><a name="operator-T"></a>Q3DeepCopy::operator T ()</h3>

106

<p>Returns a deep copy of the encapsulated data.</p>

107

<h3 class="fn"><a name="operator-eq"></a>Q3DeepCopy<T> & Q3DeepCopy::operator= ( const T & <i>t</i> )</h3>

108

<p>Assigns a deep copy of <i>t</i>.</p>

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