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Q104068: DOC: Determining Message Removal from WH_GETMESSAGE Hook

Article: Q104068
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kbdocfix kb16bitonly kbHook kbSDKPlatform kbSDKWin16
Last Modified: 22-JUL-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

A WH_GETMESSAGE hook is called each time PeekMessage or GetMessage is called.
The wParam parameter of the hook indicates whether the message is being removed
from the queue or merely being looked at.

If PeekMessage is called with the PM_NOREMOVE flag, the message will not be
removed from the queue. A WH_GETMESSAGE hook is called each time PeekMessage or
GetMessage is called, and therefore the hook may be called more than once for
the same message if PeekMessage is called with PM_NOREMOVE.

The hook can determine whether the message is being removed by using the
information in the wParam parameter. wParam contains the PM_* flags that were
used in the PeekMessage call. GetMessage calls PeekMessage with the PM_REMOVE
flag. The Windows 3.1 SDK does not document the value of wParam. It will be
documented in future versions.

Note that PM_NOREMOVE is defined as 0x0000, and therefore must be used carefully
in any Boolean conditional code. Code similar to the following may be used in
the hook:

     if (wParam & PM_REMOVE)

         Message is being removed;
     else Message is being looked at but not being removed. The hook

         may be called again for the same message.

Additional query words:

======================================================================
Keywords          : kbdocfix kb16bitonly kbHook kbSDKPlatform kbSDKWin16 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1

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