Chris Jillings wrote: > > Hello, > We may need to use the version number in ClassDef. We have have a data > structure that contains classes defined with ClassDef(ClassName,1). I want > to expand the data in the class but still be able to read the data already > written. > Is there a doc which explain how to do this? The InputOutput.html > indicates it is possible but doesn't explain how to make both versions > accessible to the linker. > Hi Chris, Sorry for this late reply. I am pretty busy these days at FNAL. Yes, you should use the version_id in the ClassDef macro if you make changes in your class (adding/deleting members). You must also modify the Streamer function for your class by testing on the version_id when you read the object. See an example in the Root class TAxis at URL: http://root.cern.ch/root/html/src/TAxis.cxx.html Rene Brun
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