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169 lines
7.4 KiB
169 lines
7.4 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qdeepcopy.cpp:40 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>QDeepCopy Class</title>
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<style type="text/css"><!--
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--></style>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</font></a>
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QDeepCopy Class Reference</h1>
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<p>The QDeepCopy class is a template class which ensures that
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implicitly shared and explicitly shared classes reference unique
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data.
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<a href="#details">More...</a>
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<p>All the functions in this class are <a href="threads.html#reentrant">reentrant</a> when Qt is built with thread support.</p>
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<p><tt>#include <<a href="qdeepcopy-h.html">qdeepcopy.h</a>></tt>
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<p><a href="qdeepcopy-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#QDeepCopy"><b>QDeepCopy</b></a> ()</li>
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<li class=fn><a href="#QDeepCopy-2"><b>QDeepCopy</b></a> ( const T & t )</li>
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<li class=fn>QDeepCopy<T> & <a href="#operator-eq"><b>operator=</b></a> ( const T & t )</li>
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<li class=fn><a href="#operator-T"><b>operator T</b></a> ()</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The QDeepCopy class is a template class which ensures that
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<a href="shclass.html#implicitly-shared">implicitly shared</a> and <a href="shclass.html#explicitly-shared">explicitly shared</a> classes reference unique
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data.
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<p>
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<p>
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<p> Normally, shared copies reference the same data to optimize memory
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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.
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<p> <pre>
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// all 5 strings share the same data
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<a href="qstring.html">QString</a> s1 = "abcd";
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<a href="qstring.html">QString</a> s2 = s1;
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<a href="qstring.html">QString</a> s3 = s2;
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<a href="qstring.html">QString</a> s4 = s3;
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<a href="qstring.html">QString</a> s5 = s2;
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</pre>
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<p> QDeepCopy can be used several ways to ensure that an object
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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.
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<pre>
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// s1, s2 and s5 share the same data, neither s3 nor s4 are shared
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<a href="qstring.html">QString</a> s1 = "abcd";
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<a href="qstring.html">QString</a> s2 = s1;
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QDeepCopy<QString> s3 = s2; // s3 is a <a href="shclass.html#deep-copy">deep copy</a> of s2
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<a href="qstring.html">QString</a> s4 = s3; // s4 is a deep copy of s3
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<a href="qstring.html">QString</a> s5 = s2;
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</pre>
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<p> In the example below, <tt>s1</tt>, <tt>s2</tt> and <tt>s5</tt> share data, and <tt>s3</tt>
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and <tt>s4</tt> share data.
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<pre>
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// s1, s2 and s5 share the same data, s3 and s4 share the same data
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<a href="qstring.html">QString</a> s1 = "abcd";
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<a href="qstring.html">QString</a> s2 = s1;
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<a href="qstring.html">QString</a> s3 = QDeepCopy<QString>( s2 ); // s3 is a deep copy of s2
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<a href="qstring.html">QString</a> s4 = s3; // s4 is a <a href="shclass.html#shallow-copy">shallow copy</a> of s3
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<a href="qstring.html">QString</a> s5 = s2;
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</pre>
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<p> QDeepCopy can also provide safety in multithreaded applications
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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
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get a unique copy of the data, and that any assignments to <tt>global_string</tt> will result in a deep copy.
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<p> <pre>
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QDeepCopy<QString> global_string; // global string data
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<a href="qmutex.html">QMutex</a> global_mutex; // mutex to protext global_string
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...
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void setGlobalString( const <a href="qstring.html">QString</a> &str )
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{
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global_mutex.<a href="qmutex.html#lock">lock</a>();
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global_string = str; // global_string is a deep copy of str
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global_mutex.<a href="qmutex.html#unlock">unlock</a>();
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}
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...
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void MyThread::run()
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{
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global_mutex.<a href="qmutex.html#lock">lock</a>();
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<a href="qstring.html">QString</a> str = global_string; // str is a deep copy of global_string
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global_mutex.<a href="qmutex.html#unlock">unlock</a>();
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// process the string data
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...
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// update global_string
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setGlobalString( str );
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}
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</pre>
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<p> <b>Warning:</b> It is the application developer's responsibility to
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protect the object shared across multiple threads.
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<p> The examples above use <a href="qstring.html">QString</a>, which is an implicitly shared
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class. The behavior of QDeepCopy is the same when using explicitly
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shared classes like <a href="qbytearray.html">QByteArray</a>.
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<p> Currently, QDeepCopy works with the following classes:
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<ul>
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<li> <a href="qmemarray.html">QMemArray</a> (including subclasses like QByteArray and <a href="qcstring.html">QCString</a>)
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<li> <a href="qmap.html">QMap</a>
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<li> QString
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<li> <a href="qvaluelist.html">QValueList</a> (including subclasses like <a href="qstringlist.html">QStringList</a> and <a href="qvaluestack.html">QValueStack</a>)
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<li> <a href="qvaluevector.html">QValueVector</a>
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</ul>
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<p> <p>See also <a href="threads.html">Thread Support in Qt</a>, <a href="shared.html">Implicitly and Explicitly Shared Classes</a>, and <a href="tools.html">Non-GUI Classes</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="QDeepCopy"></a>QDeepCopy::QDeepCopy ()
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</h3>
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<p> Constructs an empty instance of type <em>T</em>.
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<h3 class=fn><a name="QDeepCopy-2"></a>QDeepCopy::QDeepCopy ( const T & t )
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</h3>
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<p> Constructs a <a href="shclass.html#deep-copy">deep copy</a> of <em>t</em>.
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<h3 class=fn><a name="operator-T"></a>QDeepCopy::operator T ()
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</h3>
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<p> Returns a <a href="shclass.html#deep-copy">deep copy</a> of the encapsulated data.
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<h3 class=fn><a href="qdeepcopy.html">QDeepCopy</a><T> & <a name="operator-eq"></a>QDeepCopy::operator= ( const T & t )
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</h3>
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<p> Assigns a <a href="shclass.html#deep-copy">deep copy</a> of <em>t</em>.
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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