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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| Yes
| Import Library
| user32.lib
| Header File
| winuser.h
| Unicode
| WinNT
| Platform Notes
| None
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SetWindowsHookEx
The SetWindowsHookEx function installs an application-defined hook procedure into a hook chain. An
application installs a hook procedure to monitor the system for certain types
of events. A hook procedure can monitor events associated either with a
specific thread or with all threads in the system. This function supersedes the SetWindowsHook function.
HHOOK SetWindowsHookEx(
int idHook,
| // type of hook to install
| HOOKPROC lpfn,
| // address of hook procedure
| HINSTANCE hMod,
| // handle of application instance
| DWORD dwThreadId
| // identity of thread to install hook for
| );
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Parameters
idHook
Specifies the type of hook procedure to be installed. This parameter can be
one of the following values:
Value
| Description
| WH_CALLWNDPROC
| Installs a hook procedure that monitors messages before the system sends them
to the destination window procedure. For more information, see the CallWndProc hook procedure.
| WH_CALLWNDPROCRET
| Installs a hook procedure that monitors messages after they have been
processed by the destination window procedure. For more information, see the CallWndRetProc hook procedure.
| WH_CBT
| Installs a hook procedure that receives notifications useful to a
computer-based training (CBT) application. For more information, see the CBTProc hook procedure.
| WH_DEBUG
| Installs a hook procedure useful for debugging other hook procedures. For more
information, see the DebugProc hook procedure.
| WH_GETMESSAGE
| Installs a hook procedure that monitors messages posted to a message queue.
For more information, see the GetMsgProc hook procedure.
| WH_JOURNALPLAYBACK
| Installs a hook procedure that posts messages previously recorded by a
WH_JOURNALRECORD hook procedure. For more information, see the JournalPlaybackProc hook procedure.
| WH_JOURNALRECORD
| Installs a hook procedure that records input messages posted to the system
message queue. This hook is useful for recording macros. For more information, see
the JournalRecordProc hook procedure.
| WH_KEYBOARD
| Installs a hook procedure that monitors keystroke messages. For more
information, see the KeyboardProc hook procedure.
| WH_MOUSE
| Installs a hook procedure that monitors mouse messages. For more information,
see the MouseProc hook procedure.
| WH_MSGFILTER
| Installs a hook procedure that monitors messages generated as a result of an
input event in a dialog box, message box, menu, or scroll bar. For more
information, see the MessageProc hook procedure.
| WH_SHELL
| Installs a hook procedure that receives notifications useful to shell
applications. For more information, see the ShellProc hook procedure.
| WH_SYSMSGFILTER
| Installs a hook procedure that monitors messages generated as a result of an
input event in a dialog box, message box, menu, or scroll bar. The hook
procedure monitors these messages for all applications in the system. For more
information, see the SysMsgProc hook procedure.
|
lpfn
Points to the hook procedure. If the dwThreadId parameter is zero or specifies the identifier of a thread created by a
different process, the lpfn parameter must point to a hook procedure in a dynamic-link library (DLL).
Otherwise, lpfn can point to a hook procedure in the code associated with the current
process.
hMod
Identifies the DLL containing the hook procedure pointed to by the lpfn parameter. The hMod parameter must be set to NULL if the dwThreadId parameter specifies a thread created by the current process and if the hook
procedure is within the code associated with the current process.
dwThreadId
Specifies the identifier of the thread with which the hook procedure is to be
associated. If this parameter is zero, the hook procedure is associated with
all existing threads.
Return Values
If the function succeeds, the return value is the handle of the hook
procedure.
If the function fails, the return value is NULL.
Remarks
An error may occur if the hMod parameter is NULL and the dwThreadId parameter is zero or specifies the identifier of a thread created by another
process.
Chaining to the next hook procedure (that is, calling the CallNextHookEx function) is optional. An application or library can call the next hook
procedure either before or after any processing in its own hook procedure. Although
chaining to the next hook is optional, it is highly recommended; otherwise, the
other applications that have installed hooks will not receive hook
notifications and may behave incorrectly as a result.
Before terminating, an application must call the UnhookWindowsHookEx function to free system resources associated with the hook.
The scope of a hook depends on the hook type. Some hooks can be set only with
system scope; others can also be set for only a specific thread, as shown in
the following list:
Hook
| Scope
| WH_CALLWNDPROC
| Thread or system
| WH_CBT
| Thread or system
| WH_DEBUG
| Thread or system
| WH_GETMESSAGE
| Thread or system
| WH_JOURNALPLAYBACK
| System only
| WH_JOURNALRECORD
| System only
| WH_KEYBOARD
| Thread or system
| WH_MOUSE
| Thread or system
| WH_MSGFILTER
| Thread or system
| WH_SHELL
| Thread or system
| WH_SYSMSGFILTER
| System only
|
For a specified hook type, thread hooks are called first, then system hooks.
The system hooks are a shared resource, and installing one affects all
applications. All system hook functions must be in libraries. System hooks should be
restricted to special-purpose applications or to use as a development aid during
application debugging. Libraries that no longer need a hook should remove the
hook procedure.
See Also
CallNextHookEx, CallWndProc, CallWndRetProc, CBTProc, DebugProc, GetMsgProc, JournalPlaybackProc, JournalRecordProc, KeyboardProc, MouseProc, MessageProc, ShellProc, SysMsgProc, UnhookWindowsHookEx
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