FIX: Bad POINT Structure in MSG Returned by GetCurrentMessage (135913)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Professional Edition 2.0
- Microsoft Visual C++, 32-bit Professional Edition 2.1
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.
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.
| Modification Type: | Major | Last Reviewed: | 10/17/2003 |
|---|
| Keywords: | kbArchitecture kbbug kbDocView kbfix kbNoUpdate kbVC200fix kbVC220fix KB135913 |
|---|
|