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 WM_NULL

The WM_NULL message 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.

Parameters

• wParam
  This parameter is not used.
• lParam
  This parameter is not used.

Return Value

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.

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Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time