A Negative Experience in Getting Messages

Recently WinDevs, the guys in charge of developing the Getting Started content for native developers on MSDN, and I had a short conversation relating to message loops. They're in the process of creating a Win32 tutorial in the vein of TheForgers teaching the basics of creating a small Direct2D drawing app. The message loop used in their tutorials is the ubiquitous:


MSG msg;
while(GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}


On a forum I visit, one of the denizens had pointed out in response to an unrelated query that the GetMessage documentation states -1 can be returned on failure and that the loop above should not be used, instead advising programmers to use:


MSG msg;
BOOL bRet;
while( (bRet = GetMessage( &msg, NULL, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}


As the tutorial is aimed at beginners and no doubt intended to teach best practices, I mentioned the contradictory advice to them. After a bit of investigation, they've since explained the incongruity. MSDN mentions as examples that an invalid HWND and an invalid message pointer can be causes of a -1 return. Being curious about such things and not entirely trusting of MSDN's words, I wondered what exactly causes such a return...

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