JournalRecordProc

The JournalRecordProc hook procedure is an application-defined or library-defined callback function used with the SetWindowsHookEx function. The function records messages the system removes from the system message queue. Later, an application can use a JournalPlaybackProc hook procedure to play back the messages.

The HOOKPROC type defines a pointer to this callback function. JournalRecordProc is a placeholder for the application-defined or library-defined function name.

LRESULT CALLBACK JournalRecordProc(
  int code,       // hook code
  WPARAM wParam,  // not used
  LPARAM lParam   // message being processed
);

Parameters

code

[in] Specifies how to process the message. This parameter can be one of the following values.

Value	Meaning
HC_ACTION	The lParam parameter is a pointer to an EVENTMSG structure containing information about a message removed from the system queue. The hook procedure must record the contents of the structure by copying them to a buffer or file.
HC_SYSMODALOFF	A system-modal dialog box has been destroyed. The hook procedure must resume recording.
HC_SYSMODALON	A system-modal dialog box is being displayed. Until the dialog box is destroyed, the hook procedure must stop recording.

If code is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.

wParam

This parameter is not used.

lParam

[in] Pointer to an EVENTMSG structure that contains the message to be recorded.

Return Values

The return value is ignored.

Remarks

A JournalRecordProc hook procedure must copy but not modify the messages. After the hook procedure returns control to the system, the message continues to be processed.

Install the JournalRecordProc hook procedure by specifying the WH_JOURNALRECORD hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.

A JournalRecordProc hook procedure does not need to live in a dynamic-link library. A JournalRecordProc hook procedure can live in the application itself.

Unlike most other global hook procedures, the JournalRecordProc and JournalPlaybackProc hook procedures are always called in the context of the thread that set the hook.

An application that has installed a JournalRecordProc hook procedure should watch for the VK_CANCEL virtual keycode (which is implemented as the CTRL+BREAK key combination on most keyboards). This virtual keycode should be interpreted by the application as a signal that the user wishes to stop journal recording. The application should respond by ending the recording sequence and removing the JournalRecordProc hook procedure. Removal is important. It prevents a journaling application from locking up the system by hanging inside a hook procedure.

This role as a signal to stop journal recording means that a CTRL+BREAK key combination cannot itself be recorded. Since the CTRL+C key combination has no such role as a journaling signal, it can be recorded. There are two other key combinations that cannot be recorded: CTRL+ESC and CTRL+ALT+DEL. Those two key combinations cause the system to stop all journaling activities (record or playback), remove all journaling hooks, and post a WM_CANCELJOURNAL message to the journaling application.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winuser.h; include Windows.h.

See Also

Hooks Overview, Hook Functions, CallNextHookEx, EVENTMSG, JournalPlaybackProc, SetWindowsHookEx, WM_CANCELJOURNAL