<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/kernel/qguardedptr.cpp:40 --> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>TQGuardedPtr Class</title> <style type="text/css"><!-- fn { margin-left: 1cm; text-indent: -1cm; } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } body { background: #ffffff; color: black; } --></style> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr bgcolor="#E5E5E5"> <td valign=center> <a href="index.html"> <font color="#004faf">Home</font></a> | <a href="classes.html"> <font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"> <font color="#004faf">Functions</font></a> </td> <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQGuardedPtr Class Reference</h1> <p>The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects. <a href="#details">More...</a> <p><tt>#include <<a href="qguardedptr-h.html">ntqguardedptr.h</a>></tt> <p><a href="qguardedptr-members.html">List of all member functions.</a> <h2>Public Members</h2> <ul> <li class=fn><a href="#TQGuardedPtr"><b>TQGuardedPtr</b></a> ()</li> <li class=fn><a href="#TQGuardedPtr-2"><b>TQGuardedPtr</b></a> ( T * p )</li> <li class=fn><a href="#TQGuardedPtr-3"><b>TQGuardedPtr</b></a> ( const TQGuardedPtr<T> & p )</li> <li class=fn><a href="#~TQGuardedPtr"><b>~TQGuardedPtr</b></a> ()</li> <li class=fn>TQGuardedPtr<T> & <a href="#operator-eq"><b>operator=</b></a> ( const TQGuardedPtr<T> & p )</li> <li class=fn>TQGuardedPtr<T> & <a href="#operator-eq-2"><b>operator=</b></a> ( T * p )</li> <li class=fn>bool <a href="#operator-eq-eq"><b>operator==</b></a> ( const TQGuardedPtr<T> & p ) const</li> <li class=fn>bool <a href="#operator!-eq"><b>operator!=</b></a> ( const TQGuardedPtr<T> & p ) const</li> <li class=fn>bool <a href="#isNull"><b>isNull</b></a> () const</li> <li class=fn>T * <a href="#operator--gt"><b>operator-></b></a> () const</li> <li class=fn>T & <a href="#operator*"><b>operator*</b></a> () const</li> <li class=fn><a href="#operator-T-*"><b>operator T *</b></a> () const</li> </ul> <hr><a name="details"></a><h2>Detailed Description</h2> The TQGuardedPtr class is a template class that provides guarded pointers to TQObjects. <p> <p> A guarded pointer, <tt>TQGuardedPtr<X></tt>, behaves like a normal C++ pointer <tt>X*</tt>, except that it is automatically set to 0 when the referenced object is destroyed (unlike normal C++ pointers, which become "dangling pointers" in such cases). <tt>X</tt> must be a subclass of <a href="ntqobject.html">TQObject</a>. <p> Guarded pointers are useful whenever you need to store a pointer to a TQObject that is owned by someone else and therefore might be destroyed while you still hold a reference to it. You can safely test the pointer for validity. <p> Example: <pre> TQGuardedPtr<TQLabel> label = new <a href="ntqlabel.html">TQLabel</a>( 0, "label" ); label->setText( "I like guarded pointers" ); delete (TQLabel*) label; // simulate somebody destroying the label if ( label) label->show(); else <a href="ntqapplication.html#qDebug">tqDebug</a>("The label has been destroyed"); </pre> <p> The program will output <tt>The label has been destroyed</tt> rather than dereferencing an invalid address in <tt>label->show()</tt>. <p> The functions and operators available with a TQGuardedPtr are the same as those available with a normal unguarded pointer, except the pointer arithmetic operators (++, --, -, and +), which are normally used only with arrays of objects. Use them like normal pointers and you will not need to read this class documentation. <p> For creating guarded pointers, you can construct or assign to them from an X* or from another guarded pointer of the same type. You can compare them with each other using <a href="#operator-eq-eq">operator==</a>() and <a href="#operator!-eq">operator!=</a>(), or test for 0 with <a href="#isNull">isNull</a>(). And you can dereference them using either the <tt>*x</tt> or the <tt>x->member</tt> notation. <p> A guarded pointer will automatically cast to an X*, so you can freely mix guarded and unguarded pointers. This means that if you have a TQGuardedPtr<TQWidget>, you can pass it to a function that requires a <a href="ntqwidget.html">TQWidget</a>*. For this reason, it is of little value to declare functions to take a TQGuardedPtr as a parameter; just use normal pointers. Use a TQGuardedPtr when you are storing a pointer over time. <p> Note again that class <em>X</em> must inherit <a href="ntqobject.html">TQObject</a>, or a compilation or link error will result. <p>See also <a href="objectmodel.html">Object Model</a>. <hr><h2>Member Function Documentation</h2> <h3 class=fn><a name="TQGuardedPtr"></a>TQGuardedPtr::TQGuardedPtr () </h3> <p> Constructs a 0 guarded pointer. <p> <p>See also <a href="#isNull">isNull</a>(). <h3 class=fn><a name="TQGuardedPtr-2"></a>TQGuardedPtr::TQGuardedPtr ( T * p ) </h3> <p> Constructs a guarded pointer that points to same object as <em>p</em> points to. <h3 class=fn><a name="TQGuardedPtr-3"></a>TQGuardedPtr::TQGuardedPtr ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) </h3> <p> Copy one guarded pointer from another. The constructed guarded pointer points to the same object that <em>p</em> points to (which may be 0). <h3 class=fn><a name="~TQGuardedPtr"></a>TQGuardedPtr::~TQGuardedPtr () </h3> <p> Destroys the guarded pointer. Just like a normal pointer, destroying a guarded pointer does <em>not</em> destroy the object being pointed to. <h3 class=fn>bool <a name="isNull"></a>TQGuardedPtr::isNull () const </h3> <p> Returns <tt>TRUE</tt> if the referenced object has been destroyed or if there is no referenced object; otherwise returns FALSE. <h3 class=fn><a name="operator-T-*"></a>TQGuardedPtr::operator T * () const </h3> <p> Cast operator; implements pointer semantics. Because of this function you can pass a TQGuardedPtr<X> to a function where an X* is required. <h3 class=fn>bool <a name="operator!-eq"></a>TQGuardedPtr::operator!= ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) const </h3> <p> Inequality operator; implements pointer semantics, the negation of <a href="#operator-eq-eq">operator==</a>(). Returns TRUE if <em>p</em> and this guarded pointer are not pointing to the same object; otherwise returns FALSE. <h3 class=fn>T & <a name="operator*"></a>TQGuardedPtr::operator* () const </h3> <p> Dereference operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer. <h3 class=fn>T * <a name="operator--gt"></a>TQGuardedPtr::operator-> () const </h3> <p> Overloaded arrow operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer. <h3 class=fn><a href="ntqguardedptr.html">TQGuardedPtr</a><T> & <a name="operator-eq"></a>TQGuardedPtr::operator= ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) </h3> <p> Assignment operator. This guarded pointer then points to the same object as <em>p</em> points to. <h3 class=fn><a href="ntqguardedptr.html">TQGuardedPtr</a><T> & <a name="operator-eq-2"></a>TQGuardedPtr::operator= ( T * p ) </h3> This is an overloaded member function, provided for convenience. It behaves essentially like the above function. <p> Assignment operator. This guarded pointer then points to the same object as <em>p</em> points to. <h3 class=fn>bool <a name="operator-eq-eq"></a>TQGuardedPtr::operator== ( const <a href="ntqguardedptr.html">TQGuardedPtr</a><T> & p ) const </h3> <p> Equality operator; implements traditional pointer semantics. Returns TRUE if both <em>p</em> and this guarded pointer are 0, or if both <em>p</em> and this pointer point to the same object; otherwise returns FALSE. <p> <p>See also <a href="#operator!-eq">operator!=</a>(). <!-- eof --> <hr><p> This file is part of the <a href="index.html">TQt toolkit</a>. Copyright © 1995-2007 <a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center> <table width=100% cellspacing=0 border=0><tr> <td>Copyright © 2007 <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> <td align=right><div align=right>TQt 3.3.8</div> </table></div></address></body> </html>