[ros-dev] RE: [ros-diffs] [mbosma] 20543: fix typos.

[Murphy, Ged (Bolton)]

Thomas Weidenmueller wrote

> Murphy, Ged (Bolton) wrote:
> > This should really be
> >  
> > while( GetMessage( &msg, NULL, 0, 0 ) > 0 )
> >  
> > as GetMessage returns <0 on failure.
> > It will then break on failure or WM_QUIT
> >  
> >  Just being anal though as GetMessage should never really fail  ;)
> 
> See
> http://msdn.microsoft.com/library/default.asp?url=/library/en-
> us/winui/WinUI/WindowsUserInterface/Windowing/MessagesandMessa
> geQueues/MessagesandMessageQueuesReference/MessagesandMessageQ
> ueuesFunctions/GetMessage.asp
> 
> The loop shouldn't be broken if GetMessage returns -1.
> 
> - Thomas


True, I suppose it depends on the reasoning behind the GetMessage error.

MSDN does have this to say:

"Warning  
Because the return value can be nonzero, zero, or -1, avoid code like this:

while (GetMessage( lpMsg, hWnd, 0, 0)) ..."


For a bit of light hearted fun, here is the MSDN suggestion:

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


which, IIRC (I don't have a compiler to hand) would throw up 'assignment in
expression' errors with our MSVC /w4 setting. We would therefore need
something like :


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

Which has suddenly become rather long for a normally simple message loop
routine ..... LOL
A nice case for a #pragma warning() ..... or reduce the warning level for
non core components (ping)

Ged




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