apd.htm

A very good resource on Visual C++ 6.0 environment. It teaches through step by step approach and fin

<P><A HREF="javascript:popUp('xduvc11.gif')"><B>FIG. D.11</B></A><B> </B><I>All the
registers are available for examination.</I></P>
<P><B>The Disassembly Window&#160;&#160;</B>By default, the Disassembly window comes
up full screen, replacing the C++ code in the main working area. You can see the
assembly language statements generated for your C++ code, shown in Figure D.12. Debugging
at the assembly level is beyond the scope of this book, though perhaps you might
be curious to see the assembly code generated for parts of your program.</P>
<P><A HREF="javascript:popUp('xduvc12.gif')"><B>FIG. D.12</B></A><B> </B><I>You can
debug the assembler that was generated for you.</I></P>
<P>
<H2><A NAME="Heading9"></A>Using MFC Tracer</H2>
<P>The MFC Tracer utility is a standalone application with an integrated menu item
in the Developer Studio. To run it, choose Tools, MFC Tracer. Figure D.13 shows the
Tracer dialog that appears.</P>
<P><A HREF="javascript:popUp('xduvc13.gif')"><B>FIG. D.13</B></A><B> </B><I>A standalone
utility simplifies setting trace flags.</I></P>
<P>Tracer doesn't do very much: It's just an easy way to set trace flags that govern
the kind of debug output you get. Try setting all the flags on and running ShowString,
simply starting it up and shutting it down. Turn off a few flags and see how the
output changes.</P>
<P>With all the trace flags on, your application will be slow. Use Tracer to set
only the ones you're interested in, while you're interested in them. It's much easier
than changing a variable on- the-fly.</P>
<P>
<H2><A NAME="Heading10"></A>Defining a Dump Member Function</H2>
<P>All MFC classes have a Dump() member function. When things go wrong, some error-handling
code calls this function to show you the object's contents. You can write Dump()
functions for your objects, too. Although you won't normally call these functions
yourself, you could do so as part of your own error handling.</P>
<P>MFC classes inherit Dump() from Cobject, where it is defined like this:</P>
<P>
<PRE>virtual void Dump(CDumpContext&amp; dc ) const;
</PRE>
<P>The keyword virtual suggests you should override the method in your derived classes,
and const indicates that Dump() will not modify the object state.</P>
<P>Like trace and assert statements, the Dump() member function disappears in a release
build. This saves users seeing output they can't deal with and makes a smaller, faster,
release version for you. You have to make this happen yourself for any Dump() function
you write, with conditional compilation, as discussed in the &quot;Adding Debug-Only
Features&quot; section of Chapter 24.</P>
<P>In the header file, declare Dump() like this:</P>
<P>
<PRE>class CNewClass : public CObject
{
public:
     // other class stuff
     #ifdef _DEBUG
     virtual void Dump( CDumpContext&amp; dc) const
     #endif
     // ...
};
</PRE>
<P>In the implementation file, the definition, which includes a code body, might
look like this:</P>
<P>
<PRE>#include &quot;cnewclass.h&quot;
#ifdef _DEBUG
void CNewClass::Dump( CDumpContext&amp; dc ) const
{
     CObject::Dump( dc );     // Dump parent;
     // perhaps dump individual members, works like cout
     dc &lt;&lt; &quot;member: &quot; &lt;&lt; /* member here */ endl;
}
#endif
</PRE>
<P>As you see in the code for the Dump() function, writing the code is much like
writing to standard output with the cout object or serializing to an archive. You
are provided with a CDumpContext object called dc, and you send text and values to
that object with the &lt;&lt; operator. If this is unfamiliar to you, read Chapter
7, &quot;Persistence and File I/O.&quot;</P>
<P>
<H3><A NAME="Heading11"></A>An Example Using CDumpContext, CFile, and axfDump</H3>
<P>The sample application in this section uses the MFC debugging class CDumpContext
and the global axfDump object. The debug window output from this demo and the output
CFile code are in Listing D.1. To run this application yourself, create a console
application as described in Chapter 28, &quot;Future Explorations,&quot; and create
an empty C++ source file called Dump.cpp. Enter this code, build, and run a debug
version of the project.</P>
<P>When linking a debug version of this product, if you receive error messages that
refer to _beginthreadex and _endthreadex, you need to change some settings. By default,
console applications are single-threaded, but MFC is multithreaded. By including
afx.h and bringing in MFC, this application is making itself incompatible with the
single-threaded default. To fix this, choose Project Settings and click the C/C++
tab. From the drop-down box at the top of the dialog box, choose Code Generation.
In the drop-down box labeled Use Runtime Library, choose Debug Multithreaded. (Figure
D.15 shows the completed dialog.) Click OK and rebuild the project. You should usually
change the settings for release as well, but because the calls to Dump() aren't surrounded
by tests of _DEBUG, this code won't compile a release version anyway.</P>
<P>
<H4>Listing D.1&#160;&#160;Dump.Cpp--Demonstrating the MFC Debugging Class CDumpContext
and the Output CFile Code</H4>
<PRE>#include &lt;afx.h&gt;
// _DEBUG defined for debug build
class CPeople : public CObject
{
public:
    // constructor
        CPeople( const char * name );
        // destructor
        virtual ~CPeople();
        #ifdef _DEBUG
            virtual void Dump(CDumpContext&amp; dc) const;
        #endif
    private:
        CString * person;
    };
    // constructor
    CPeople::CPeople( const char * name) : person( new CString(name)) {};
    // destructor
    CPeople::~CPeople(){ delete person; }
#ifdef _DEBUG
    void CPeople::Dump( CDumpContext&amp; dc ) const
    {
        CObject::Dump(dc);
        dc &lt;&lt; person-&gt;GetBuffer( person-&gt;GetLength() + 1);
    }
#endif
int main()
    {
        CPeople person1(&quot;Kate Gregory&quot;);
        CPeople person2(&quot;Clayton Walnum&quot;);
        CPeople person3(&quot;Paul Kimmel&quot;);
        // Use existing afxDump with virtual dump member function
        person1.Dump( afxDump );
        // Instantiate a CFile object
        CFile dumpFile(&quot;dumpout.txt&quot;, CFile::modeCreate | 
            CFile::modeWrite);
        if( !dumpFile )
        {
            afxDump &lt;&lt; &quot;File open failed.&quot;;
        }
        else
        {
            // Dump with other CDumpContext
            CDumpContext context(&amp;dumpFile);
            person2.Dump(context);
        }
        return 0;
</PRE>
<PRE>    }
</PRE>
<P>This single file contains a class definition, all the code for the class member
functions, and a main() function to run as a console application. Each of these parts
of the file is explained in the next few paragraphs. The class is a simple wrapper
around a CString pointer, which allocates the CString with new in the constructor
and deletes it in the destructor. It's so simple that it's actually useless for anything
other than demonstrating the Dump() function.</P>
<P>First, the &lt;afx.h&gt; header file is included, which contains the CObject class
definition and provides access to afxDump.</P>
<P>Next, this code defines the class CPeople derived from CObject. Notice the placement
of the override of the virtual Dump() method and the conditional compiler wrap. (Any
calls to Dump() should be wrapped in the same way, or that code will not compile
in a release build.)</P>
<P>Following the constructor and destructor comes the code for CPeople::Dump(). Notice
how it, too, is wrapped in conditional compiler directives. The call to CObject::Dump()
takes advantage of the work done by the MFC programmers, dumping information all
objects keep.</P>
<P>Finally, the main() function exercises this little class. It creates three instances
of the CPeople class and dumps the first one.</P>
<P>For the second CPeople object, this code creates and opens a CFile object by passing
a text string to the constructor. If the open succeeds, it creates a CDumpContextObject
from the file and passes this context to Dump instead of the usual afxDump().</P>
<P>If you run this program, you'll see output like that in Figure D.14. The file
dumpout.txt will contain these lines:</P>
<P>
<PRE>a CObject at $71FDDC
Clayton Walnum
</PRE>
<P><A HREF="javascript:popUp('xduvc14.gif')"><B>FIG. D.14</B></A><B> </B><I>Using
the afxDump context sends your output to the Debug window.</I></P>
<P>The first line of the output, to both the debug window and the file, came from
CObject::Dump() and gives you the object type and the address. The second line is
from your own code and is simply the CString kept within each CPeople.</P>
<P><A HREF="javascript:popUp('xduvc15.gif')"><B>FIG. D.15</B></A><B> </B><I>To use
MFC in a console application, change to the multithreaded runtime library.</I></P>
<P>Now that you've seen the basic tools of debugging in action, you're ready to put
them to work in your own applications. You'll find errors quickly, understand other
people's code, and see with your own eyes just how message-routing and other behind-the-scenes
magic really occur. If you find yourself enjoying debugging, don't worry--no one
else has to know!</P>
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