Microsoft KB Archive/135913

= FIX: Bad POINT Structure in MSG Returned by GetCurrentMessage =

Article ID: 135913

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++ 2.0 Professional Edition

 Microsoft Visual C++ 2.1 

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This article was previously published under Q135913



SYMPTOMS
MFC provides a function called GetCurrentMessage that returns a pointer to a MSG structure encapsulating the current message being processed. The MSG structure contains a member variable (pt), of type POINT that contains incorrect values.



CAUSE
The GetCurrentMessage function fills in the POINT structure with the following line of code: *((DWORD*)&pThreadState->m_lastSentMsg.pt) = ::GetMessagePos; This code was correct in the 16-bit version of Visual C++ because a POINT structure was made up of two intergers (int) that were each 16-bits. Thus the size of a POINT was the same as a DWORD.

However, in the 32-bit version of Windows and of the Visual C++ compiler, a POINT structure is made up of two LONGs, each 32-bits, so the total size of a POINT is now 64-bits and the above assignment is not valid.



RESOLUTION
To obtain the correct value for the point in the current MSG you can use MFC's overridden CPoint constructor which takes a DWORD as an argument. For example: CPoint pt(::GetMessagePos); // Now pt has the correct values Please note that because the GetCurrentMessage function returns a pointer to a 'const' MSG structure, you can't change the pt member of the message structure.

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STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Visual C++ version 2.2.

Additional query words: 2.00 2.10 3.00 3.10

Keywords: kbarchitecture kbbug kbdocview kbfix kbnoupdate kbvc200fix kbvc220fix KB135913

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