JournalPlaybackProc callback function

Article
03/30/2018

Warning

Journaling Hooks APIs are unsupported starting in Windows 11 and will be removed in a future release. Because of this, we highly recommend calling the SendInput TextInput API instead.

An application-defined or library-defined callback function used with the SetWindowsHookEx function. Typically, an application uses this function to play back a series of mouse and keyboard messages recorded previously by the JournalRecordProc hook procedure. As long as a JournalPlaybackProc hook procedure is installed, regular mouse and keyboard input is disabled.

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

Syntax

LRESULT CALLBACK JournalPlaybackProc(
  _In_ int    code,
       WPARAM wParam,
  _In_ LPARAM lParam
);

Parameters

code [in]
Type: int

A code the hook procedure uses to determine how to process the message. 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. This parameter can be one of the following values.

Value	Meaning
HC_GETNEXT 1	The hook procedure must copy the current mouse or keyboard message to the EVENTMSG structure pointed to by the lParam parameter.
HC_NOREMOVE 3	An application has called the PeekMessage function with wRemoveMsg set to PM_NOREMOVE, indicating that the message is not removed from the message queue after PeekMessage processing.
HC_SKIP 2	The hook procedure must prepare to copy the next mouse or keyboard message to the EVENTMSG structure pointed to by lParam. Upon receiving the HC_GETNEXT code, the hook procedure must copy the message to the structure.
HC_SYSMODALOFF 5	A system-modal dialog box has been destroyed. The hook procedure must resume playing back the messages.
HC_SYSMODALON 4	A system-modal dialog box is being displayed. Until the dialog box is destroyed, the hook procedure must stop playing back messages.

wParam
Type: WPARAM

This parameter is not used.
lParam [in]
Type: LPARAM

A pointer to an EVENTMSG structure that represents a message being processed by the hook procedure. This parameter is valid only when the code parameter is HC_GETNEXT.

Return value

Type: ****

Type: LRESULT

To have the system wait before processing the message, the return value must be the amount of time, in clock ticks, that the system should wait. (This value can be computed by calculating the difference between the time members in the current and previous input messages.) To process the message immediately, the return value should be zero. The return value is used only if the hook code is HC_GETNEXT; otherwise, it is ignored.

Remarks

A JournalPlaybackProc hook procedure should copy an input message to the lParam parameter. The message must have been previously recorded by using a JournalRecordProc hook procedure, which should not modify the message.

To retrieve the same message over and over, the hook procedure can be called several times with the code parameter set to HC_GETNEXT without an intervening call with code set to HC_SKIP.

If code is HC_GETNEXT and the return value is greater than zero, the system sleeps for the number of milliseconds specified by the return value. When the system continues, it calls the hook procedure again with code set to HC_GETNEXT to retrieve the same message. The return value from this new call to JournalPlaybackProc should be zero; otherwise, the system will go back to sleep for the number of milliseconds specified by the return value, call JournalPlaybackProc again, and so on. The system will appear to be not responding.

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.

After the hook procedure returns control to the system, the message continues to be processed. If code is HC_SKIP, the hook procedure must prepare to return the next recorded event message on its next call.

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

If the user presses CTRL+ESC OR CTRL+ALT+DEL during journal playback, the system stops the playback, unhooks the journal playback procedure, and posts a WM_CANCELJOURNAL message to the journaling application.

If the hook procedure returns a message in the range WM_KEYFIRST to WM_KEYLAST, the following conditions apply:

The paramL member of the EVENTMSG structure specifies the virtual key code of the key that was pressed.
The paramH member of the EVENTMSG structure specifies the scan code.
There's no way to specify a repeat count. The event is always taken to represent one key event.

Requirements

Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Winuser.h (include Windows.h)

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