FIX: Using CString or Collection Class Links in CWinApp Code

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, version 1.0
  

SYMPTOMS

Using a CString object or collection object (CObList, CStringArray, and so forth) in an application forces the code for CWinApp to be linked into the application whether or not a CWinApp object is defined. The CWinApp code requires that SHELL.LIB and COMMDLG.LIB be specified in the link options.

If you are not linking with SHELL.LIB and COMMDLG.LIB, and you use a CString or collection object without a CWinApp object, you will receive the following linker errors:

   error L2029: 'GETFILETITLE' : unresolved external
   error L2029: 'REGSETVALUE' : unresolved external
   error L2029: 'REGQUERYVALUE' : unresolved external
   error L2029: 'DRAGFINISH' : unresolved external
   error L2029: 'DRAGQUERYFILE' :unresolved external

CAUSE

The problem described above is caused by a compiler/linker bug. To understand the problem, consider the code:

   extern int somevariable;
   __inline void func(){ somevariable=1;}
   void main(){ return;}

The Microsoft Foundation Class (MFC) libraries do something similar in the AFXWIN.INL file located in the \MSVC\MFC\INCLUDE directory. The code is as follows:

   _AFXWIN_INLINE CWinApp* AFXAPI AfxGetApp()
     { return afxCurrentWinApp; }
   _AFXWIN_INLINE HINSTANCE AFXAPI AfxGetInstanceHandle()
        { ASSERT(afxCurrentInstanceHandle != NULL);
          return afxCurrentInstanceHandle; }
   _AFXWIN_INLINE HINSTANCE AFXAPI AfxGetResourceHandle()
     { ASSERT(afxCurrentResourceHandle != NULL);
       return afxCurrentResourceHandle; }
   _AFXWIN_INLINE void AFXAPI AfxSetResourceHandle(HINSTANCE hInstResource)
     { ASSERT(hInstResource != NULL); afxCurrentResourceHandle =
       hInstResource; }
  _AFXWIN_INLINE const char* AFXAPI AfxGetAppName()
     { ASSERT(afxCurrentAppName != NULL); return afxCurrentAppName; }

RESOLUTION

To work around this problem, do one of the following:

• Link with SHELL.LIB and COMMDLG.LIB and ignore the fact that some extra code will be linked into your application.

  -or-

• Migrate your application to MFC by using a CWinApp object.

STATUS

Microsoft has confirmed this to be a problem with Microsoft Foundation Classes version 2.0. This problem has been corrected in version 2.5 of the Microsoft Foundation Classes, which is included with Visual C++ version 1.5.

MORE INFORMATION

To reproduce the problem, compile and link the sample program below:

Sample Code

/* Compile options needed:  /AM /GA

*               link with MAFXCW.LIB
*/

#include <afxwin.h>
void main(void)