KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q88190: PRB: DLL System Hook Function Not Affecting Apps System-Wide

Article: Q88190
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly kbHook kbSDKPlatform
Last Modified: 11-JUN-1999

3.10
WINDOWS
kbprg kbprb

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

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

SYMPTOMS
========

When you are trying to install a system hook function with SetWindowsHookEx in a
Dynamic-Link Library (DLL), the hook function is executed only within the
calling application even though it is supposed to affect all applications
system-wide.

CAUSE
=====

In Windows 3.0, the minimum required compile option to generate the appropriate
entry/exit code sequence for a Windows-based application is the /Gw switch.

With Microsoft C/C++ version 7.0, however, the documentation states that the /Gw
and /GW switches should be used only for applications that must run in real mode
Windows. Because real mode is no longer available in Windows 3.1, most programs
should now be built using the /GA switch (/GD for DLLs). The C 7.0 /GA and /GD
switches require that exported functions (especially callback functions) be
explicitly marked as __export if the switch is to affect them.

RESOLUTION
==========

If the DLL containing the hook function is compiled with the /GD switch, the
hook function should be explicitly marked with the __export keyword:

     LRESULT FAR PASCAL __export CbtFunc (int Code,

                                       WPARAM wParam, LPARAM lParam);

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

Additional query words: 3.10

======================================================================
Keywords          : kb16bitonly kbHook kbSDKPlatform 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbprb

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

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.