QDataStream format change in Qt3.1

Matthias Ettrich ettrich at trolltech.com
Thu Sep 12 13:44:02 BST 2002

On Thursday 12 September 2002 14:01, Lubos Lunak wrote:
>  (*) Actually the only change between versions 4 and 5 seems to be QImage,
> so for practical purposes it probably can be considered compatible, but
> still, the problem of future versions remains.

The change only effects QImage (meaning also QPixmap).  We should marshall 
(read: should have marshalled) a datastream version, but that's too late now.

The problem isn't as serious as it looks, because most the marshalling 
functions are inside Qt. If you run a KDE 3.0.3 application linked to Qt 3.1, 
those apps will use the newer format as well => no problem.

Note that the DCOP protocol only is about sending a blob of bytes marked with 
a name to a certain object. It's KDE's protocol on top of those that 
interprets the name as a function name with parameters and the blob of bytes 
as the arguments written with a qdatastream. 

I do not foresee any futher format changes for the types we are using, meaning 
the problem is minor. The trouble with QImage was that libpng doesn't handle 
null images very well and we needed a way to stream a null image without 
error messages and unpredictable behaviour.


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