Microsoft KB Archive/148304

= INFO: Frequently Encountered MFC 3.x to 4.0 Porting Issues =

Article ID: 148304

Article Last Modified on 11/21/2006

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APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 4.0 Standard Edition

 Microsoft Visual C++ 4.1 Subscription

 Microsoft Visual C++ 4.2 Enterprise Edition

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 5.0 Enterprise Edition</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul> </li></ul>

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<div class="notice_section">

This article was previously published under Q148304

<div class="summary_section">

SUMMARY
This article lists some of the most frequently encountered bugs, problems, and other issues that you may experience when attempting to port an application written with MFC 3.x (the MFC included with Visual C++ 2.x) to work with MFC 4.0 (the MFC included with Visual C++ 4.0).

<ol> === General Issues ===

Window classes are no longer pre-registered by MFC.BUG: The first control on CFormView gets OnSetFocus before OnInitialUpdate executes.CWinApp::m_templateList no longer exists.BUG: The CString += operator may break with null strings.BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  Window classes are no longer pre-registered by MFC.BUG: The first control on CFormView gets OnSetFocus before OnInitialUpdate executes.CWinApp::m_templateList no longer exists.BUG: The CString += operator may break with null strings.BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  BUG: The first control on CFormView gets OnSetFocus before OnInitialUpdate executes.CWinApp::m_templateList no longer exists.BUG: The CString += operator may break with null strings.BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  CWinApp::m_templateList no longer exists.BUG: The CString += operator may break with null strings.BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  BUG: The CString += operator may break with null strings.BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically.BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  BUG: OnInitMenuPopup now deletes the menu temp map before returning.Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject.BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  BUG: Default dialog-based application doesn't work in Win32s.

CPropertySheet
CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  CPropertySheet always changes its font to the default font.Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  Property sheet modifications should be done in OnInitDialog after a call to the base class.CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li>  CPropertySheet::DoModal causes first chance exception in Windows 95.Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> Property Sheets now have a minimum width.

DLLs
MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> MFC threads cannot be created during DLL startup.Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions.BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> BUG: DoModal may fail in MFC extension DLLs.

CStatusBar and CToolBar
CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> CToolbar::SetSizes and button sizing.

CFileDialog
No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> No need to replace the MFC-supplied CFileDialog hook procedure.CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> CFileDialog is always a child of the Explorer dialog window.CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> CFileDialog member functions GetFileName and GetFileTitle reversed.

MFC ODBC
BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li> BUG: Dynasets with CLongBinary fields throw an exception.

MFC OLE
No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments. </li> <li>No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments.</li></ol>

<div class="moreinformation_section">

General Issues
1. Window classes are no longer pre-registered by MFC:

Previous to version 4.0, MFC pre-registered four window (WNDCLASS) classes, as documented in MFC Technical Note number 1. These window classes were AfxWnd, AfxFrameOrView, AfxMDIFrame, and AfxControlBar. Most code (such as the ONETIME sample) that prevented more than one instance of an application relied on these classes.

Now, as of version 4.0, these four classes are not registered until a window of that type is created. Windows based on a custom WNDCLASS that fill in information from the MFC window classes will likely just fail to show, sending the message that window creation failed. GetLastError returns the value 0x57F (ERROR_WNDCLASS_DOES_NOT_EXIST) to the debug output window if MFC tracing is turned on.

From version 4.0 on, you need to provide all of the necessary information when registering custom window classes with RegisterClass or AfxRegisterClass. Do not rely on ::GetClassInfo to retrieve class values for MFC window classes.

For additional information, please see MFC Technical Note 1 and the following articles in the Microsoft Knowledge Base:

140596 MFC 4.0 No Longer Pre-Registers Window Classes

141752 SAMPLE: Limiting 32-bit Applications to a Single Instance

2. BUG: The first control on CFormView gets OnSetFocus before OnInitialUpdate executes: This causes problems if there is code in OnSetFocus that refers to CWnd objects that won't be subclassed until the call to the base class OnInitDialog. This problem may also occur in any other handler called as a result of the control getting the focus. For example, radio buttons will generate a BN_CLICKED when they get the focus.

For additional information and a workaround, please see the following article in the Microsoft Knowledge Base:

142274 FIX: Assertion Failure When Handling xN_SETFOCUS in CFormView

3. CWinApp::m_templateList no longer exists:

The m_templateList member variable of CWinApp was undocumented in MFC versions prior to 4.0 but was used frequently enough to be called a porting issue. Microsoft recommends that you use the GetFirstDocTemplatePosition and GetNextDocTemplate member functions of CWinApp to gain access to the templates for an application.

For additional information, please see the following article in the Microsoft Knowledge Base:

106455 How to Acquire a List of All CDocument Objects

4. BUG: The CString += operator may break with null strings: The particular sequence of events that result in this bug is complex. There is a bug in the MFC source code that incorrectly handles the case when a null string is used with the += operator.

For additional information, please see the following article in the Microsoft Knowledge Base:

142385 FIX: Using CString::operator+= May Cause an Access Violation

5. BUG: OnWndMsg case for WM_xSCROLL messages breaks when scroll bars are scrolled programmatically: Code was added in MFC 4.0 to pass the full 32 bits of position (when available) on to the OnxScroll handlers because the WM_xSCROLL messages can only pack 16 bits of position information. Unfortunately the code that was added breaks whenever an application programmatically scrolls a scroll bar by sending a WM_xSCROLL message to itself by way of SendMessage.

For additional information, please see the following article in the Microsoft Knowledge Base:

147684 FIX: Sending WM_xSCROLL Message Causes Invalid ASSERT

6. BUG: OnInitMenuPopup now deletes the menu temp map before returning: In MFC version 4.0, calls to AfxLockTempMaps and AfxUnlockTempMaps were added to CWnd::OnInitMenuPopup. When AfxUnlockTempMaps is called, MFC's temporary object map reference count will go to zero causing all temporary MFC objects to be deleted. When the call to OnInitMenuPopup returns, the CMenu pointer passed in to OnInitMenuPopup (which is a temporary pointer) will be invalid.

For additional information, please see the following article in the Microsoft Knowledge Base:

141532 FIX: OnInitMenuPopup Deletes Temporary Objects

7. Documented CRuntimeClass::m_pfnConstructObject is now m_pfnCreateObject: m_pfnConstructObject was a documented member variable of CRuntimeClass in MFC versions prior to 4.0, but the name was changed to reflect the change in parameters and return value. The documentation included with Visual C++ 4.0 was not updated to reflect this change and incorrectly references the old function name. 8. BUG: Default dialog-based application doesn't work in Win32s: When AppWizard generates a dialog-based application, it uses a DIALOGEX resource for the main dialog. Win32s, however, does not support DIALOGEX resources. As a result, the dialog box looks incorrect in Win32s. This can be fixed by removing the WS_EX_APPWINDOW style from within the dialog editor and by changing the DIALOGEX statement to a DIALOG statement in the .rc file.

For additional information, please see the Visual C++ Readme file and the following article in the Microsoft Knowledge Base:

138971 BUG: Default Dialog-Based Application Doesn't Work in Win32s

CPropertySheet
Much of the MFC implementation of CPropertySheet has changed to now wrap the Windows Property Sheet common control. There have been some formatting and sizing changes, but more importantly, if code made use of any of the private MFC implementations of CPropertySheet, the code will likely break as most of the undocumented members of that class are no longer there.

9. CPropertySheet always changes its font to the default font:

Even if the font of the property pages is changed in the Resource Editor, property pages will be displayed at run time with the system font. If it is necessary to change the font, call SetFont in OnInitDialog; then use an appropriate MoveWindow to resize the sheet and move and resize all the controls on the page. Also, the property sheet is set back to its original size whenever a page is activated, so it will be necessary to resize the page in response to a click on the tab control.

For additional information, please see the following article in the Microsoft Knowledge Base:

142170 SAMPLE: PRPFONT - How to Set CPropertySheet Fonts

10. Property sheet modifications should be done in OnInitDialog after call to base class:

During CPropertySheet::OnInitDialog, the property sheet is resized and the four standard buttons (OK, Cancel, Apply, and Help) are hidden at the bottom of modeless property sheets. The proper place to modify the size of the sheet or to customize the four property sheet buttons is in OnInitDialog after the call to the base class. In previous versions of MFC, it was common practice to hide some of the buttons shown with a modal property sheet in OnCreate. These buttons can now be easily removed by modifying styles in the PROPSHEETHEADER structure CPropertySheet::m_psh.

For additional information, please see the following articles in the Microsoft Knowledge Base:

140585 PRB: Resizing CPropertySheet in OnInitDialog Does Not Work

141039 How to Hide the Apply Button in CPropertySheet

11. CPropertySheet::DoModal causes first chance exception on Windows 95:

A first chance exception occurs on Windows 95 because the property page sets required styles in the dialog resource. The operating system needs to handle this, so the message can be ignored. If you surround the DoModal call with a try/catch(...) block in an effort to handle the exception yourself, you will get a stack fault. 12. Property Sheets now have a minimum width:

The minimum width of a CPropertySheet window is the size of the four buttons (OK, Cancel, Apply, and Help) that would show up along the bottom of a modal property sheet. This width applies even to modeless property sheets, which do not show the four buttons along the bottom.

DLLs
13. MFC threads cannot be created during DLL startup:

Although not a good idea, it was possible to create a thread during the startup of an MFC DLL in previous versions of MFC. This includes calling AfxBeginThread or CWinThread::CreateThread in DllMain, RawDllMain, InitInstance in the DLL, or in any functions called by these. Due to synchronization of MFC thread startup code and blocking at DllMain during DLL_PROCESS_ATTACH and DLL_THREAD_ATTACH, this is no longer permitted. MFC 4.0 DLLs that attempt to do this will hang when loaded by an application.

For additional information, please see the following article in the Microsoft Knowledge Base:

142243 PRB: Cannot Create an MFC Thread During DLL Startup

14. Regular DLLs using MFC in the Shared Library require AFX_MODULE_STATE in exported functions:

Previously, the USRDLL model required that MFC be statically linked to the DLL. It is now possible to link dynamically to the Mfc40.dll from a Regular DLL (the new term for _USRDLLs). The caveat is that to convert a _USRDLL to be a "Regular DLL using MFC in a Shared Library," you need to make sure that you manage your module state information correctly. The single line: AFX_MANAGE_STATE(AfxGetStaticModuleState); should be added to the beginning of any function exported from the DLL that operates on MFC objects.

The following problems are likely to occur if the module state is not switched appropriately:
 * Dialogs and windows fail at creation in a DLL because of missing resources.
 * Functions for the wrong application object are called and cause stack overflow or unpredictable results.
 * Unrecognized run-time class information.
 * Bad window-to-MFC object handle map linkage.

For additional information, please see MFC Technical Note 58 (TN058) and the following article in the Microsoft Knowledge Base:

140850 How to Convert DLLTRACE to Use MFC in Shared Library

15. BUG: DoModal may fail in MFC extension DLLs: When MFC 4.0 creates a dialog box, it passes the current instance handle to the ::CreateDialogIndirect Windows API - which creates the dialog instead of the resource handle for the DLL. The template for the dialog was already loaded by MFC from the correct extension DLL. However, Windows will look in the .exe file specified by the instance handle for any extra resources indicated on the template. Windows will not find them if they are in the DLL, and the dialog creation will fail. To work around this problem, the current instance handle should be temporarily switched before any calls to DoModal. Extra resources include such things as the dialog's menu, custom controls, or an icon on the dialog.

For additional information, please see the following article in the Microsoft Knowledge Base:

147384 FIX: Icons, Bitmaps, & Menus Not Displayed in an AFXDLL Dialog

CStatusBar and CToolBar
Like CPropertySheet, these MFC classes now wrap the functionality of the Win32 common controls. Any code that relied on or modified the private, undocumented implementation of these classes will likely break when compiled for MFC 4.0. These two common controls support a greater range of common customizations than did the previous default MFC implementation, and they do not require significant overrides of the MFC source for such tasks as constructing palette bars or making resizable toolbars. If needed, the old implementation of these two classes is still present as the COldToolBar and COldStatusBar classes. These implementations can be found in the OLDBARS sample project. 16. CToolbar::SetSizes and button sizing:

Toolbars now require that the width of the button size be at least 7 pixels greater than the image size. The documentation that ships with Visual C++ 4.0 was not updated to reflect this change and is incorrect. An ASSERT that MFC version 4.0 uses to verify correct parameters in SetSizes also incorrectly checks for the old value of 6. There are other limits on the sizes of the toolbar, buttons, and images, but these are correctly covered by ASSERT statements in the MFC source and have not changed since MFC 3.x.

For additional information, please see the following article in the Microsoft Knowledge Base:

141444 DOC: Incorrect Documentation for CToolBar::SetSizes

CFileDialog
17. No need to replace the MFC-supplied CFileDialog hook procedure:

MFC always specifies its own hook procedure (_AfxCommDlgProc) for the Open File Dialog during the construction of the CFileDialog object so that it can properly route notifications for the dialog to the proper handlers. As of MFC 4.x, this hook procedure is used to subclass the CFileDialog object to the Open File Dialog window. If the hook procedure is replaced, this subclass procedure won't occur, so any attempt to use the CFileDialog or an embedded control variable on it (as if it were a window) will fail.

18. CFileDialog is always a child of the Explorer dialog window:

When you use the Explorer-style CFileDialog (which in Windows 95 you are doing by default), MFC 4.0 assumes the Explorer model of customization. This implies that custom improvements to the File dialog are included on a separate template that is added around the standard Explorer dialog. In MFC 4.0, the actual CFileDialog window is a child dialog of the main File Common Dialog, even if you are not providing a template to customize the dialog. Therefore, if you have a need to alter the standard Explorer interface by moving or hiding controls, prefix all GetDlgItem calls to Explorer controls with GetParent. For example, this expression: GetParent->GetDlgItem(IDOK) will return a pointer to the Open/Save button on the Explorer dialog. However, this is not recommended because code that relies on the details of the standard Explorer dialog controls will break if the Explorer layout is changed in the future.

This default can be changed by removing the OFN_EXPLORER style. For more information, see the following Microsoft Knowledge Base article:

131225 PRB: CFileDialog::DoModal Does Not Display FileOpen Dialog

19. CFileDialog member functions GetFileName and GetFileTitle reversed:

In MFC 4.0, for the file C:\Article.txt:


 * CFileDialog::GetFileName returns Article.txt.
 * CFileDialog::GetFileTitle returns Article.

Previous versions of MFC returned exactly the opposite. These functions have been changed to work in a manner similar to the Win32 API functions of the same names. However, the documentation included with Visual C++ 4.0 was not updated to reflect these changes and is incorrect.

For additional information, please see the Visual C++ Readme file and the following article in the Microsoft Knowledge Base:

142203 DOCERR: GetFileTitle & GetFileName Docs Are Switched

MFC ODBC
20. BUG: Dynasets with CLongBinary fields throw exception: An MFC ODBC application that uses dynaset recordsets with CLongBinary-bound fields worked in Visual C++ 2.x, but it now throws an exception in Visual C++ 4.0 when the recordset is opened. The exception is thrown from CRecordset::InitRecord.

For additional information, please see the following article in the Microsoft Knowledge Base:

141303 FIX: Dynasets w/ CLongBinary Fields Throws Incorrect Exception

MFC OLE
21. No more Mfcans32.dll, so OLE functions in MFC applications require Unicode arguments:

In MFC 3.x, a special DLL was used (Mfcans32.dll) to convert automatically between Unicode and MBCS when OLE interfaces were called. MFC 4.0 does not use this DLL; instead, it talks directly to the Unicode OLE interfaces. To handle this change, MFC applications now must pass the correct type of parameters - whether Unicode or MBCS - to OLE functions. MFC 4.0 has provided a number of macros that make this task easier.

For more information please see MFC Technical Note 59.

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