PRB: PostMessage() Returns 0, Indicating Failure

ID: Q36584

The information in this article applies to:

Microsoft Windows Software Development Kit (SDK) versions 3.1, 3.0

SYMPTOMS

PostMessage(hWnd,wMsg,wParam,lParam) returns 0, indicating failure.

CAUSE

PostMessage(hWnd,wMsg,wParam,lParam) returns 0, indicating failure, for one of the following two reasons:

The window handle (hWnd parameter to PostMessage()) receiving the message is -1. If this is the case, the message (wMsg) is broadcast to all windows.
The window to receive the message has a full application queue.

Note that PostMessage() does not return NULL if the hWnd parameter in the PostMessage() call is an invalid window handle. Also note that IsWindow() can be called to verify whether a given handle is indeed a valid window handle.

Additional query words:

Keywords          : kb16bitonly kbSDKPlatform kbGrpUser kbWndw kbWndwMsg 
Issue type        : kbprb

Last Reviewed: January 3, 1999