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WM_NULL message

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Performs no operation. An application sends the WM_NULL message if it wants to post a message that the recipient window will ignore.

A window receives this message through its WindowProc function.

#define WM_NULL                         0x0000

Parameters

wParam

This parameter is not used.

lParam

This parameter is not used.

Return value

Type: LRESULT

An application returns zero if it processes this message.

Remarks

For example, if an application has installed a WH_GETMESSAGE hook and wants to prevent a message from being processed, the GetMsgProc callback function can change the message number to WM_NULL so the recipient will ignore it.

As another example, an application can check if a window is responding to messages by sending the WM_NULL message with the SendMessageTimeout function.

Requirements

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

See also

Windows Overview