DOCUMENT:Q104068  22-JUL-1999  [win16sdk]
TITLE   :DOC: Determining Message Removal from WH_GETMESSAGE Hook
PRODUCT :Microsoft Windows Software Development Kit
PROD/VER:WINDOWS:3.1
OPER/SYS:
KEYWORDS:kbdocfix kb16bitonly kbHook kbSDKPlatform kbSDKWin16

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

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

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

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1999.