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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>Refactoring Existing Code</h1>
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[ <a href="motif-walkthrough-6.html">Previous: Using TQt Main Window Classes</a> ]
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[ <a href="motif-walkthrough.html">Home</a> ]
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[ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ]
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<p> In the author's view, the existing code is slightly disorganized.
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Even though the code <em>does</em> work, some cleanups and reorganization
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can only help with readability and maintainability. The steps
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described below are not necessary during the migration process but are
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included for completeness.
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<p> <h2> Migrating Data Structures to C++
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</h2>
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<a name="1"></a><p> The <tt>Page</tt> data structure is an opaque data type. The real data
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structure is called <tt>PageRec</tt>; <tt>Page</tt> defined to be a pointer to a
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<tt>PageRec</tt>. In addition, we have the <tt>AllocPage()</tt> function that
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allocates and initializes memory for a <tt>PageRec</tt> struct.
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<p> With C++, we can do this in the constructor. We can also write a
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destructor which automatically frees all resources in the <tt>PageRec</tt>,
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instead of having to do it in several different places.
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<p> The <tt>PageRec</tt> struct declaration is removed from <tt>page.h</tt>. We
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declare a <tt>Page</tt> struct with the same data members as <tt>PageRec</tt>, a
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constructor and a destructor.
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<p>
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<pre></pre>
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<p> The existing <tt>pages</tt>, <tt>currentPage</tt> and <tt>maxpages</tt> global variables
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are removed from the source files. We replace them with <tt>extern</tt>
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declarations in <tt>page.h</tt>.
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<p> <pre></pre>
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<p> The global variable instantiations are placed in <tt>todo.cpp</tt>.
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<p> Each source file contains function declarations that deal with the
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global <tt>Page</tt> related variables. We remove these declarations from
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the source files and declare them once in the <tt>page.h</tt> header file.
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<p> <pre></pre>
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<p> Now that <tt>Page</tt> has a constructor, we remove the <tt>AllocPage()</tt>
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function. It is no longer needed. The calls to <tt>AllocPage()</tt> are
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replaced with <tt>'new Page()'</tt> in the <tt>NewPage()</tt>, <tt>DeletePage()</tt>
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and <tt>ReadDB()</tt> functions. We also replace the code to deallocate
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pages with <tt>delete pages[X]</tt>, where <em>X</em> is the appropriate index
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value. This is done in the <tt>ReadDB</tt> and <tt>DeletePage()</tt> functions.
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<p> Code that accesses the global <tt>pages</tt> variable does not need to be
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modified since the data members of the <tt>Page</tt> struct did not change.
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The existing code will continue to work.
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<p> The <tt>OptionsRec</tt> struct declared in <tt>page.h</tt> is also updated,
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following the same pattern as the <tt>Page</tt> struct above.
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<p> <pre></pre>
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<p> The global variable instantiation is also placed in <tt>todo.cpp</tt>.
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<p> Code that accesses the global <tt>options</tt> variable does not need to be
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modified since the data members of the <tt>Options</tt> struct did not
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change. The existing code will continue to work.
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<p> <h2> Using <em>new</em> and <em>delete</em>
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</h2>
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<a name="2"></a><p> The destructors of the <tt>Page</tt> and <tt>Options</tt> structs use <em>delete</em>
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instead of <tt>XtFree()</tt> to deallocate all <tt>char*</tt> members. This is a
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necessary change since we are migrating away from Xt/Motif. We need
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to fix existing code that modifies the <tt>Page</tt> struct members to use
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<em>new</em> and <em>delete</em> ( instead of <tt>XtMalloc()</tt>, <tt>XtNewString()</tt> and
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<tt>XtFree()</tt> ).
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<p> The <tt>PageChange()</tt> function in <tt>todo.cpp</tt> simply saves the contents
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and cursor position of current page before calling <tt>SetPage()</tt>. We
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use <em>new</em> and <em>delete</em> when modifying members of the <tt>Page</tt> struct.
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<p>
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<pre></pre>
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<p> When storing the context of the <tt>XmText</tt> widget, we use <a href="ntqcstring.html#qstrdup">qstrdup</a>()
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to make a copy of the string returned by the <tt>XmTextGetString()</tt>
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function.
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<p> <pre></pre>
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<p> The <tt>ReadDB()</tt> function in <tt>io.cpp</tt> needs similar changes. We
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replace all use of <tt>XtMalloc()</tt> and <tt>XtNewString()</tt> with <em>new</em> and
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<a href="ntqcstring.html#qstrdup">qstrdup</a>(), respectively.
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<p> This needs to be done just after opening the file.
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<p>
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<pre></pre>
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<p> ... when starting a new page ...
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<p> <pre>
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...
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</pre>
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<pre></pre>
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<p> ... and when reading in the label and tab texts/
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<p> <pre>
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...
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</pre>
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<pre></pre><pre>
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...
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</pre>
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<pre></pre><pre>
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...
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</pre>
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<pre></pre>
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<p> The <tt>ReadDB()</tt> function uses <tt>XtRealloc()</tt> to expand the data
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storage buffer. Unfortunately, C++ does not provide a way to
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reallocate an existing block of data, so we have to do this ourselves.
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<p> <pre></pre>
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<p> There is also one occurence in <tt>ReadDB()</tt> where we call <tt>XtMalloc()</tt>
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with an argument of 2. This was done when a file could not be read.
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Creating an empty string is not necessary, so we remove this code
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instead of using <em>new</em>.
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<p> <pre></pre>
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<p> The <tt>SaveDB()</tt> function in <tt>io.cpp</tt> also needs these changes. We
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change one occurence of <tt>XtFree()</tt> to <em>delete</em>.
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<p> <pre></pre>
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<p> Finally, We need to replace two occurences of <tt>XtNewString()</tt> in the <tt>main()</tt> function in <tt>todo.cpp</tt>.
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<p>
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<pre></pre>
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<p> <h2> Moving Existing Code
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</h2>
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<a name="3"></a><p> The rest of the refactoring process involves moving existing code into
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new places. Currently, each function in the <tt>mainwindow.ui.h</tt> file
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simply calls the old callback handlers present in the other files.
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Instead of calling the old callback functions, the implementations are
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moved accordingly.
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<p> <center><table cellpadding="4" cellspacing="2" border="0">
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<tr bgcolor="#a2c511"> <th valign="top">Function <th valign="top">Original File <th valign="top">Moved to Function
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<tr bgcolor="#f0f0f0"> <td valign="top"><tt>New()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileNew()</tt>
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<tr bgcolor="#d0d0d0"> <td valign="top"><tt>Open()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileOpen()</tt>
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<tr bgcolor="#f0f0f0"> <td valign="top"><tt>SaveIt()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::fileSave()</tt>
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<tr bgcolor="#d0d0d0"> <td valign="top"><tt>Save()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileSaveAs()</tt>
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<tr bgcolor="#f0f0f0"> <td valign="top"><tt>ShowPrintDialog()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::filePrint()</tt>
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<tr bgcolor="#d0d0d0"> <td valign="top"><tt>EditPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selProperties()</tt>
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<tr bgcolor="#f0f0f0"> <td valign="top"><tt>NewPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selNewPage()</tt>
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<tr bgcolor="#d0d0d0"> <td valign="top"><tt>DeletePage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selDeletePage()</tt>
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</table></center>
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<p> The <tt>Print()</tt> callback function is still used by the <em>Print</em>
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dialog, so we move it into <tt>mainwindow.ui.h</tt> and make it <tt>static</tt>.
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<p> Previously, the <tt>Open()</tt>, <tt>Save()</tt>, <tt>EditPage()</tt> and <tt>DeletePage()</tt>
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functions created dialogs with <em>client_data</em> as the parent argument.
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Since we have moved the code directly into the <em>Main Window</em>
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implementation, we create these dialogs with <em>this</em> as the parent
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argument.
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<p> The <tt>PageChange()</tt> callback function is moved from <tt>actions.cpp</tt>
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to <tt>todo.cpp</tt> and made <tt>static</tt> since it is not used anywhere else.
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<p> Earlier modifications to <tt>actions.cpp</tt> caused the <tt>Trim()</tt> function
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to become redundant, so we remove it.
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<p> The <tt>MIN()</tt> and <tt>MAX()</tt> macros in <tt>todo.cpp</tt> are redundant. TQt
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provides the <tt>TQMIN()</tt> and <tt>TQMAX()</tt> macros which we will use.
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<p> Earlier modifications caused the <tt>fallback_resources</tt> array to become
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redundant, so we remove it.
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<p> In the near future, our program will not use <a href="motif-extension.html#Motif">Motif</a> any more, and we
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will no longer need to use <a href="qmotif.html">TQMotif</a>. To prepare for this, we remove the
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<tt>resources</tt> and <tt>optionDesc</tt> arrays and create the TQMotif instance
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with just the <em>APP_CLASS</em> argument.
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<p> The <tt>#include</tt> statements in the source files are mostly incorrect
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due to the refactoring changes. Many of the <tt>#include</tt> statements
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are no longer needed. The <tt>#include</tt> statements from each file are
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listed below, instead of describing which includes are removed and
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added to each file.
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<p> Includes for <tt>actions.cpp</tt>:
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<p>
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<pre></pre>
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<p> Includes for <tt>io.cpp</tt>:
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<p>
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<pre></pre><pre></pre><pre></pre>
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<p> Includes for <tt>todo.cpp</tt>:
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<p>
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<pre></pre><pre></pre><pre></pre>
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<p> Includes for <tt>mainwindow.ui.h</tt>:
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<p>
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<pre></pre><pre></pre><pre></pre><pre></pre><pre></pre>
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<p> [ <a href="motif-walkthrough-6.html">Previous: Using TQt Main Window Classes</a> ]
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[ <a href="motif-walkthrough.html">Home</a> ]
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[ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ]
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<p>
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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>TQt 3.3.8</div>
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