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FYI: MFC BUG with Win2000 and Platform SDK

Posted on 2000-02-23
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Last Modified: 2013-11-20
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In order to access Win2000 specific APIs etc, one needs the following #define in the application's stdafx.h (before any other #includes)

     #define _WIN32_WINNT 0x0500

With the latest platform SDK, this also has the side effect of changing the definition for the OPENFILENAME struct; in particular it makes it larger.  This is because of the following lines in the "CommDlg.h"

     typedef struct tagOFNA {
        DWORD        lStructSize;
...
...
        LPCSTR       lpTemplateName;
     #ifdef _MAC
        LPEDITMENU   lpEditInfo;
        LPCSTR       lpstrPrompt;
     #endif
>>>  #if (_WIN32_WINNT >= 0x0500)
>>>     void *       pvReserved;
>>>     DWORD        dwReserved;
>>>     DWORD        FlagsEx;
>>>  #endif // (_WIN32_WINNT >= 0x0500)
     } OPENFILENAMEA, *LPOPENFILENAMEA;

This means when the definition of class CFileDialog is compiled, it's m_ofn member will have a different size than in the MFC dlls.  This is because CFileDialog is defined as:

     class CFileDialog : public CCommonDialog
     {
          DECLARE_DYNAMIC(CFileDialog)
     public:
     // Attributes
>>>       OPENFILENAME m_ofn; // open file parameter block
...
...
     };

When a CFileDialog is used in your code and is destructed, the wrong offsets into memory for member varialbes will be unsed, and in particular, the m_strFilter will not destruct properly.

The work-around for this is to #undef _WIN32_WINNT before the #include <afxext.h> in the application's stdafx.h:

>>>  #define _WIN32_WINNT 0x0500   /* allow Win2000 specific calls */
     #define VC_EXTRALEAN          // Exclude rarely-used stuff from Windows
headers
     #include <afxwin.h>         // MFC core and standard components
>>>  #undef _WIN32_WINNT           /* allow CFileDialog to build with the
correct size */
     #include <afxext.h>         // MFC extensions
     #include <afxdtctl.h>         // MFC support for Internet Explorer 4 Common
Controls
     #ifndef _AFX_NO_AFXCMN_SUPPORT
     #include <afxcmn.h>           // MFC support for Windows Common Controls
     #endif // _AFX_NO_AFXCMN_SUPPORT

Now, <afxext.h> will (indrectly) #include <CommDlg.h> and define CFileDIalog all without the offending _WIN32_WINNT.

NOTE: This only works because the VC_EXTRALEAN stops <afxwin.h> from including CommDlg.h earlier.

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Question by:RONSLOW
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