INF: When PostMessage() Will Return 0, Indicating Failure

ID Number: Q36584

2.03 2.10 3.00

WINDOWS

Summary:

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

for one of the following two reasons:

1. 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.

2. 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.