Microsoft KB Archive/88190

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

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Q88190

3.10 WINDOWS kbprg kbprb

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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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.

Steps to Reproduce Behavior
Additional query words: 3.10

Keywords : kb16bitonly kbHook kbSDKPlatform

Issue type : kbprb

Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310