Microsoft KB Archive/194298

= Description of the changes in MFC between Visual C++ 5.0 and Visual C++ 6.0 =

Article ID: 194298

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++ 6.0 Enterprise Edition

 Microsoft Visual C++ 6.0 Professional Edition

 Microsoft Visual C++ 6.0 Standard Edition

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

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

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

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This article was previously published under Q194298

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SUMMARY
MFC has changed substantially since it shipped in Visual C++ version 5.0. MFC 6.0 (Mfc42.dll, version 6.00.8168.0), shipping with Visual C++ 6.0, contains many new classes, new member functions, bug fixes and enhancements. This document provides an overview of the more substantial changes in MFC.

Largely, the changes made to the library fit in one of several categories. First, many changes were made in an effort to make the library more efficient. Even though MFC 6.0 has many new features, the size of the DLL is just about the same as it was in the last version. You'll notice that the statically-linked version of the library is more granular-many problems which caused unused code to be brought into the library were addressed in this version. Finally, there are many new classes and member functions in the libraries that provide for integrated access to new operating system features.

While the library has undergone some growth, you should be able to recompile your programs with the new library without changing them. Further, you should be able to install the MFC DLLs over old versions without recompiling programs which use the library.

Since some of the changes to the library were made to address very broad goals, this document contains a section on global changes. After those global changes are addressed, there's a section on each new or changed class. We've made every attempt to make this document as comprehensive as possible, but it's main purpose is to provide an aid to understanding the differences between this and the previous version of the library. Because of resource limitations, this document does not, by any means, include a comprehensive list of all bugs fixed since the last release of the library.

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Global Changes
 MFC uses __declspec(selectany). The compiler provides this __declspec to control the section in which initialized data will be placed within the executable. MFC uses the macros AFX_STATIC and AFX_STATIC_DATA to apply the modifier on initialized data which the library needs. You'll see AFX_STATIC and AFX_STATIC_DATA used aggressively throughout the library source.</li> The unused m_hInst member of the private AFX_COM class was removed. This unused variable in an MFC implementation class wasn't necessary. Code to initialize it was deleted from the library.</li> The CPushRoutingFrame and CPushRoutingView implementation classes were added to the library. These classes encapsulate code that was previously used in the OnCmdMsg handler for views and frames in MFC.</li>  Placement syntax support for global operator delete. The compiler now supports placement-syntax delete operators which properly delete memory in situations where placement syntax operator new was used. Since MFC makes heavy use of placement syntax new in both debug and non-debug builds, support for the placement syntax delete operator was added.

For example, the debug global 'operator new' function in MFC is defined as: void operator new(size_t nSize, LPCSTR lpszFileName, int nLine) because we have a overridden global 'new' operator defined, we need to define a global operator delete which also takes the same number of arguments so MFC has defined the 'delete' operator as: void operator delete(void * pData, LPCSTR /*lpszFileName */,                    int /*nLine*/) </li></ul>

Library Implementation Changes

 * Thread safety in the CThreadSlotData implementation class has improved. This fixes problems with deadlocks and thread safety usually apparent only on multiprocessor machines. CThreadSlotData is used internally by MFC to manage thread-local data for the library.
 * COMCTL preregistration code was rewritten to be more efficient. MFC will initialize the COMCTL32.DLL library appropriately as your application executes. Since a recent update to that DLL allows applications to only register window classes they need (rather than all classes supplied by the library) MFC will use the more efficient API when it is available. When the updated COMCTL32.DLL is not available, MFC falls back on its original behavior.
 * MFC.DLL build uses /DELAYLOAD linker option. The shared DLL version of MFC now uses the linker's new /DELAYLOAD option. This makes the library only load DLLs when it is necessary to actually initialize them rather than load and initialize all referenced DLLs. This significantly reduces the size of the DLL.

Collection Classes

 * MFC uses memmove where appropriate. The collection classes would sometimes use memcpy where memmove was actually required.
 * FindIndex returns NULL for negative indexes. List-based collections with a FindIndex member will return NULL if the index passed to the function is negative. In previous releases, this scenario caused a hang or an access violation.

CArchive

 * To improve runtime performance, enhancements to the class were made to avoid double-buffering while writing to or reading from the archive.
 * Don't reset schema when loading old objects. Reading code in the class would reset the expected schema number when reading older objects into memory. The buggy code caused problems when reading some partially updated file types and was fixed in this version of the library.

CAsyncSocket

 * SendTo member correctly returns errors. In previous versions of MFC, CAsyncSocket::SendTo returned FALSE for some errors. The function now returns a proper WinSock error code in all circumstances.

CCheckListBox

 * CCheckListBox features a new SetSelectionCheck member which can check (or uncheck) the selected items within the box.

CComboBox

 * MFC-created combo boxes now properly initialize their contents from data provided by the resource editor.

CControlBar

 * The new SetBorders member is a public accessor which allows other classes to set the bar's borders.
 * The new DrawGripper member function draws a "gripper", which is a user-interface clue on command bars that are movable or resizable.
 * CalcInsideRect adjusts for the correct sizing of a bar that has a gripper.
 * The CControlBar class will assert that the m_dwStyle member only contains MFC-specific bits masked by CBRS_ALL. This assertion will fire if user code sets window-style bits which is wrong.
 * The floating and docking behavior of control bars has been fixed to work acceptably on multiple monitor systems.

CDC

 * In previous versions of MFC, CDC member functions would sometimes return unpredictable values for extreme failure conditions. These functions have been cleaned up and will return the correct error code.

CTabCtrl

 * SetItemState and GetItemState member functions have been added in order to support new functionality exposed by the revised COMCTL32.DLL.

CToolBar

 * SetSizes can be called when toolbar isn't created. The function previously ASSERTed when it wasn't attached to a window, but now reacts by setting them member data of the object to reflect the size instead of moving the window's position.
 * The CToolBar class has been significantly cleaned up for efficiency and also modified to gracefully handle compatibility issues with old and new COMCTL32.DLL implementations.

CTreeCtrl

 * The GetCheck and SetCheck members have been added to support checked tree controls.

COleControl

 * The style bit fastBeginPaint is now ignored. OLE Controls are always expected to erase their background in OnDraw, as they won't receive WM_ERASEBKGND when rendering to a metafile DC.
 * The handlers for the mouse button messages in the class were rewritten to be more efficient without changing their functionality.
 * Several small bugs in the in-place activation implementation have been fixed.
 * The MFC-supplied tracker now clips properly.
 * OnSetObjectRects has been fixed. This function's implementation ignored the clipping rectangle and would cause spurious window movement (resulting in extra repaints) during windowless activation. The code has been fixed to avoid those problems.
 * The reflector window now handles WM_SIZE appropriately. Previously, the message was ignored.
 * CreateTracker/DestroyTracker now call OnSetObjectRects. Duplicated code in the CreateTracker and DestroyTracker members has been folded into OnSetObjectRects to save space. Since adding or removing the tracker does cause the objects' bounding rectangle size to change, it's appropriate that the action now cause call to OnSetObjectRects.

COleDateTime

 * Several rounding errors existed in previous versions of this class. All known rounding problems have been remedied.
 * The class now features a GetAsSystemTime member function, which can be used to convert the time object's value to a SYSTEMTIME structure.

CTime

 * The class now features a GetAsSystemTime member function, which can be used to convert the time object's value to a SYSTEMTIME structure.

CWinApp

 * MFC no longer calls CloseHandle on the m_hThread handle member of the application object. The new behavior avoids leaks and diagnostic messages.
 * Registry deletion code was cleaned up. Significant duplicated code to remove keys from the registry has been removed from the library, resulting in a space savings.
 * Applications which register themselves as a DocObject server, OAT_DOC_OBJECT_SERVER, will enter their file extension directly from the document resource string's filterExt field, if it is available. Otherwise, MFC will try to parse an extension from the filterName field.

CObject

 * Placement syntax has been added for CObject's operator delete. The compiler now supports placement-syntax delete operators which properly delete memory in situations where placement syntax operator new was used. Since MFC makes heavy use of placement syntax new in both debug and non-debug builds, support for the placement syntax delete operator was added.

CDaoDatabase

 * Not dependent on DAO 3.5. Some recent releases of MFC had problems running correctly on machines that weren't updated to DAO 3.5. Those problems have been resolved, but it is advisable to upgrade to DAO 3.5 anyway due to performance and stability improvements.

CDaoRecordset

 * IsBOF and IsEOF are now const.
 * The Unicode DFX_Text function would not allocate enough space when binding Unicode strings. This problem has been fixed.
 * A DDX routine to work with the CSlider control has been provided. The routine exchanges the slider's integer with a field in the database.

CDatabase

 * ODBC 3.0 dependency relieved. MFC DLLs previously worked only against ODBC 3.0, and are now compatible with ODBC 2.5.

CHttpFile

 * Support for log post data. The CHttpFile class now supports long post data via the SendRequestEx and EndRequest member functions.

CHttpServer

 * An overridable function named OnTerminateExtension has been provided to support the termination notification sent by newer ISAPI servers.
 * MFC will write the response stream in blocks to be compatible with HTTPS and other protocols with size limitations. The new m_dwChunkSize member variable determines the block size, and the OnWriteBody function can be overridden to alter the writing behavior.
 * A new parse map parameter type has been added. You may retrieve the raw parameters from the client by using the ITS_RAW parameter type.
 * Via the TransmitFile member and OnWriteBody override, the class now supports overlapped I/O.

CInternetFile

 * In some circumstances, the ReadString member function would truncate data read from the connection. This bug has been fixed.

CInternetSession

 * CInternetSession has new member functions to aid with the management of cookies.
 * All internet-related functions in MFC more aggressively ASSERT on the validity of memory buffer pointer parameters.
 * INTERNET_FLAG_ASYNC was never supported by MFC. The presence of this flag now causes debug builds of MFC to ASSERT.

CListCtrl

 * Member functions have been added to support virtual list views.

CMDIChildWnd

 * CMDIChildWnd features a new CreateNewChild which facilitates the creation of MDI child windows outside of the doc-view architecture.

COleDocument

 * Previous versions of MFC opened storages with STGM_SHARE_EXCLUSIVE. MFC now uses the more appropriate STGM_SHARE_DENY_WRITE flag, which allows other applications to read the storage while it is opened by the document object.

COleIPFrame

 * Menu merging, IOleCommandTarget, and command forwarding support was added to COleIPFrame in order to support DocObject containment.

CSlider

 * There's now DDX_Slider, which facilitates data exchange with an integer variable and a slider control.

CPropertyPage

 * The creation of a property sheet with pages from a DIALOGEX resource would sometimes needlessly ASSERT. The assertion has been corrected.
 * The MapWizardResult member function would sometimes return an incorrect value. This problem has been corrected.
 * Some property page creations would result in a blank dialog. This problem was fixed.
 * MFC's handler for EndDialog incorrectly returned IDCANCEL instead of PSBTN_CANCEL.
 * A property page closed with the system menu or by the user pressing the close button might not correctly set the m_nModalResult member to IDCANCEL. This has been fixed.

CRecordset

 * The RFX_Int function incorrectly handled NULL values in previous versions of the library. This problem has been corrected.

CScrollView

 * A bug that caused a bogus assert when the mouse wheel was used to scroll a CScrollView has been fixed.
 * Mouse wheel page-mode scrolling has been fixed. A bug which made page-by-page views scroll in the wrong direction has been fixed.

CString

 * CString has been modified to use an extremely fast fixed-size memory allocator. The memory allocator will work for string sizes up to 64 characters, 128 characters, 256 characters, and 512 characters to improve performance for the most commonly encountered string sizes.
 * CString now includes several new utility functions to ease string programming. Find has a new overload that takes an offset. There are length-based string constructors. Delete and Insert functions provide for removal and insertion, respectively, of characters within the string. Replace provides a way to substitute a substring for another substring, or a character for another character. TrimRight and TrimLeft now feature new overrides which can trim user-specified characters or sets of characters.
 * Format supports __int64. The Format member now supports the "%I64" formatting string for use with __int64 data types.

CView

 * The print preview bar has been restored to its rightful position-within the parent frame.

CWinThread

 * The MFC-supplied PreTranslateMessage member function is no longer responsible for canceling active tooltips. This code has been moved to CWnd::FilterToolTipMessage. This change was necessary in order to support the new tracking tooltip styles.

CWnd

 * All CWnd-derived classes will print a TRACE message upon failure in their creation functions. The message identifies the failure point and shows the last error value to aid in diagnosis.
 * The CenterWindow function has been fixed to work properly on multiple monitor machines.

New Classes

 * To support newly available common controls, the CMonthCalCtrl, CDateTimeCtrl, and CIPAddressCtrl classes have been added to the library. Appropriate overrides of DDX_ and RFX_ functions have been added to the library, as well.
 * The CReBar and CReBarCtrl classes was added to the library to provide access to the new rebar control.
 * The CHtmlView class is used to contain the Internet Explorer ActiveX Control.
 * The CPropSheetEx and CPropPageEx classes were added to support new user interface styles in the property page API.

Socket Support

 * MFC changed how WinSock specific thread state information is stored. Pointers to handle maps, instead of the handle maps themselves, are stored in the AFX_MODULE_THREAD_STATE data.

Keywords: kbhowto kbinfo kbnoupdate KB194298

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