ch28.htm

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

help is a good source of information for these three DLLs.</P>
<P>A good tool for poking around in Windows applications is the DumpBin utility,
usually found in \Program Files\Microsoft Visual Studio\VC98\Bin. DumpBin is a command
line program that shows you the imports and exports of executable files and dynamic
link libraries. The following listing is an excerpted example of the output produced
when using DumpBin to examine the executable file for Spy++, one of the utilities
provided with Visual C++.</P>
<P>
<H4>Listing 28.3&#160;&#160;Output from DumpBin</H4>
<PRE>dumpbin -imports spyxx.exe
Microsoft (R) COFF Binary File Dumper Version 6.00.8047
Copyright  Microsoft Corp 1992-1998. All rights reserved.
Dump of file spyxx.exe
File Type: EXECUTABLE IMAGE
  Section contains the following imports:
    MFC42.DLL
                44B138 Import Address Table
                452B8C Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                      Ordinal   818
                      Ordinal  4424
              ... 392 similar lines omitted ...
    MSVCRT.dll
                44B7A4 Import Address Table
                4531F8 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                  81  __set_app_type
                  6F  __p__fmode
                  6A  __p__commode
                  9D  _adjust_fdiv
                  83  __setusermatherr
                 10F  _initterm
                  58  __getmainargs
                  8F  _acmdln
                 249  exit
                 2B5  sscanf
                  49  __CxxFrameHandler
                 298  memmove
                 1B9  _splitpath
                 134  _itoa
                 159  _mbscmp
                 2C9  strtoul
                 100  _getmbcp
                 168  _mbsnbcpy
                  8E  _access
                 161  _mbsinc
                 192  _purecall
                 2B2  sprintf
                  A5  _beginthread
                  C4  _endthread
                 25E  free
                 15F  _mbsicmp
                  B7  _controlfp
                 291  malloc
                 158  _mbschr
                  F1  _ftol
                 1F3  _wcsupr
                 2EB  wcsrchr
                  63  __p___argv
                  62  __p___argc
                 2D4  toupper
                 272  iscntrl
                 2D0  time
                  55  __dllonexit
                 186  _onexit
                  CA  _except_handler3
                  2E  ?terminate@@YAXXZ
                  D3  _exit
                  48  _XcptFilter
                 1AA  _setmbcp
    MSVCIRT.dll
                44B75C Import Address Table
                4531B0 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                 194  ?str@strstreambuf@@QAEPADXZ
                 11F  ?freeze@strstreambuf@@QAEXH@Z
                 10F  ?ends@@YAAAVostream@@AAV1@@Z
                 171  ?seekp@ostream@@QAEAAV1@J@Z
                  8B  ??6ostream@@QAEAAV0@K@Z
                  87  ??6ostream@@QAEAAV0@G@Z
                  50  ??1ostrstream@@UAE@XZ
                  14  ??0ios@@IAE@XZ
                  31  ??0ostrstream@@QAE@XZ
                 1BB  _mtlock
                 1BC  _mtunlock
                  47  ??1ios@@UAE@XZ
                  8A  ??6ostream@@QAEAAV0@J@Z
                  89  ??6ostream@@QAEAAV0@I@Z
                  88  ??6ostream@@QAEAAV0@H@Z
                  85  ??6ostream@@QAEAAV0@E@Z
                  93  ??6ostream@@QAEAAV0@PBD@Z
    KERNEL32.dll
                44B084 Import Address Table
                452AD8 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                 246  SetEvent
                 136  GetProfileStringA
                 10F  GetModuleFileNameA
                  32  CreateFileA
                  19  CloseHandle
                 2AC  WideCharToMultiByte
                 1CB  MultiByteToWideChar
                  93  FindResourceA
                 272  SizeofResource
                 168  GlobalAlloc
                 173  GlobalLock
                 1AE  LoadResource
                 1BC  LockResource
                 17A  GlobalUnlock
                 16F  GlobalFree
              ... 29 similar lines omitted ...
    USER32.dll
                44B8AC Import Address Table
                453300 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                 2A5  wsprintfA
                 160  GetWindowWord
                 253  SetWindowLongA
                 158  GetWindowPlacement
                 1CF  OffsetRect
                 189  IsIconic
                 16E  InflateRect
                 240  SetRectEmpty
                  CF  EnumWindows
                  BC  EnumChildWindows
                 218  SetActiveWindow
                  EE  GetClientRect
              ... 77 similar lines omitted ...
    GDI32.dll
                44B024 Import Address Table
                452A78 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                 167  Rectangle
                 121  GetStockObject
                 17A  SelectObject
                  3D  CreatePen
                 19D  SetROP2
                  30  CreateFontIndirectA
                  36  CreateHatchBrush
                  41  CreateRectRgn
                  72  FrameRgn
                  1D  CreateBitmap
                  E8  GetDeviceCaps
                 137  GetTextMetricsA
                 130  GetTextExtentPoint32A
                  3C  CreatePatternBrush
                 14E  PatBlt
                 161  PtInRegion
                  46  CreateSolidBrush
                  4C  DeleteObject
                 111  GetObjectA
                  23  CreateCompatibleDC
                   D  BitBlt
                 118  GetPixel
                  6B  ExtTextOutA
    ADVAPI32.dll
                44B000 Import Address Table
                452A54 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference
                 148  RegCreateKeyA
                 15B  RegOpenKeyA
                 160  RegQueryInfoKeyA
                 149  RegCreateKeyExA
                 170  RegSetValueExA
                 15C  RegOpenKeyExA
                 165  RegQueryValueExA
                 145  RegCloseKey
  Summary
       17000 .data
        A000 .rdata
       10000 .rsrc
</PRE>
<PRE>       4A000 .text
</PRE>
<P>As you can see, the utility program Spy++ uses the C Runtime and Windows DLLs
extensively.</P>
<P>You can call functions from the Windows DLLs in any of your programs, and more
importantly, you can write DLLs of your own.</P>
<P>
<H3><A NAME="Heading6"></A>Making a 32-Bit DLL</H3>
<P>There are two kinds of DLLs in Visual C++: Those that use MFC and those that don't.
Each kind of DLL has its own AppWizard, as you will see shortly.</P>
<P>If you gather three or four functions into a DLL, your DLL <I>exports</I> those
functions for other programs to use. Quite often a DLL will also <I>import</I> functions
from other DLLs to get its work done.</P>
<P><B>Importing and Exporting Functions&#160;&#160;</B>To designate a symbol as exportable,
use the following syntax:</P>
<P>
<PRE>__declspec(dllexport) data_type int var_name; // for variables
</PRE>
<P>or</P>
<P>
<PRE>__declspec(ddlexport) return_type func_name( [argument_list ] ); 
// for functions
</PRE>
<P>Importing functions is almost identical: Simply replace the keyword tokens, __declspec(dllexport)
with __declspec(dllimport). Use an actual function and variable to demonstrate the
syntax this time:</P>
<P>
<PRE>__declspec(dllimport) int referenceCount;
__declspec(dllimport) void DiskFree( lpStr Drivepath );
</PRE>


<BLOCKQUOTE>
	<P>
<HR>
<STRONG>TIP:</STRONG> Two underscores precede the keyword __declspec. 
<HR>


</BLOCKQUOTE>

<P>By convention, Microsoft uses a header file and a preprocessor macro to make the
inclusion of DLL declarations much simpler. The technique requires that you make
a preprocessor token using a unique token--the header filename works easily and requires
very little in the way of memorization--and define a macro that will replace the
token with the correct import or export statement. Thus, assuming a header file named
Diskfree.h, the preprocessor macro in the header file would be as follows.</P>
<P>
<H4>Listing 28.4&#160;&#160;Diskfree.h</H4>
<PRE>// DISKFREE.H - Contains a simpler function for returning the amount of 
// free disk space.
#ifndef __DISKFREE_H
#define __DISKFREE_H
#ifndef __DISKFREE__
#define DISKFREELIB __declspec(dllimport)
#else
#define DISKFREELIB __declspec(dllexport)
#endif
// Use the macro to control an import or export declaration.
DISKFREELIB unsigned long DiskFree( unsigned int drive ); 
// (e.g. 0 = A:, 1 = B:, 2 = C:
</PRE>
<PRE>#endif
</PRE>
<P>By including the header file, you can let the preprocessor decide whether DiskFree
is being imported or exported. Now you can share the header file for the DLL developer
and the DLL user, and that means fewer maintenance headaches.</P>
<P><B>Creating the DiskFree DLL&#160;&#160;</B>The DiskFree utility provides a simple
way to determine the amount of free disk space for any given drive. The underlying
functionality is the GetDiskFreeSpace() function found in Kernel32.dll.</P>
<P>To create a non-MFC DLL, choose File, New, click the Projects tab, select Win32
Dynamic Link Library from the list on the left, and enter DiskFree for the project
name. Click OK and the AppWizard dialog box, shown in Figure 28.4, appears. Choose
An Empty DLL project, and your project is created with no files in it.</P>
<P>Add a C++ header file called DiskFree.h to the project and type in the code from
Listing 28.5. Add a C++ source file called DiskFree.cpp and type in the code from
Listing 28.6.</P>
<P>
<H4>Listing 28.5&#160;&#160;DiskFree.h</H4>
<PRE>#ifndef __DISKFREE_H
#define __DISKFREE_H
#ifndef __DISKFREE__
#define __DISKFREELIB__ __declspec(dllimport)
#else
#define __DISKFREELIB__ __declspec(dllexport)
#endif
// Returns the amount of free space on drive number (e.g. 0 = A:, 1= B:, 
// 2 = c:)
__DISKFREELIB__ unsigned long DiskFree( unsigned int drive );
</PRE>
<PRE>#endif
</PRE>
<H4>Listing 28.6&#160;&#160; DiskFree.cpp</H4>
<PRE>#include &lt;afx.h&gt;
#include &lt;winbase.h&gt;     // Declares kernel32 GetDiskFreeSpace 
#define __DISKFREE__     // Define the token before including the library
#include &quot;diskfree.h&quot;
// Returns the amount of free space on drive number
// (e.g. 0 = A:, 1= B:, 2 = c:)
__DISKFREELIB__ unsigned long DiskFree( unsigned int drive )
{