Re: Problem with the Streamer function of a class derived from TDirectory...

Pierre-Luc,

Instead of TDirectory, you should derive from TDirectoryFile. In version 5.16, TDirectory
became an abstract interface. See 5.16 Release Notes at: http://root.cern.ch/root/Version516.news.html

Rene Brun

Pierre-Luc Drouin wrote:
> Hi,
>
> I have derived a class from TDirectory and I am trying to store and
> retrieve an instance of this class to/from a ROOT file.
>
> I am using the autogenerated Streamer function and when I call
> TDirectory
> <http://root.cern.ch/root/html514/src/TDirectory.cxx.html#OUS8P>(const
> char *name, const char *title, Option_t
> <http://root.cern.ch/root/html514/ListOfTypes.html#Option_t>
> *classname, TDirectory
> <http://root.cern.ch/root/html514/TDirectory.html>* initMotherDir)
> from the constructor of my class, I set classname to the name of my
> class.
>
> I do not get any warning/error message when I Write the instance in
> the root file, but I get the following error when I try to load the
> instance using TFile::Get:
>
> Error in <TBuffer::ReadVersion>: Could not find the StreamerInfo with
> a checksum of 0 for the class "TUUID" in file.root.
> Error in <TBuffer::CheckByteCount>: object of class TUUID read too few
> bytes: 22 instead of 898023151
> Error in <TBuffer::CheckByteCount>: Byte count probably corrupted
> around buffer position 85:
> 898023151 for a possible maximum of 17
> SysError in <TFile::Seek>: cannot seek to position 60235645022633984
> in file file.root, retpos=-1 (Invalid argument)
> Error in <TFile::ReadBuffer>: error reading all requested bytes from
> file file.root, got 186 of 2687036
>
> Here is the code of a class that allows to reproduce the problem:
>
> class QMyDir: public TDirectory
> {
> public:
> QMyDir():TDirectory(){}
>
> QMyDir(const QMyDir& newqds):TDirectory(){*this=newqds; }
>
> QMyDir(const char *name, const char *title, TDirectory* motherDir =
> 0):TDirectory(name,title,"QMyDir",motherDir){}
>
> virtual ~QMyDir(){}
>
> QMyDir& operator=(const QMyDir &rhs){fprintf(stderr,"Warning:
> TDirectory::operator= function is private and cannot be called by
> derived class QMyDir\n"); return *this;}
>
> private:
>
> ClassDef(QMyDir,1) //QSigEx Data Structure Class
> };
>
> Here is the code of the autogenerated Streamer function:
>
> void QMyDir::Streamer(TBuffer &R__b)
> {
> // Stream an object of class QMyDir.
>
> UInt_t R__s, R__c;
> if (R__b.IsReading()) {
> Version_t R__v = R__b.ReadVersion(&R__s, &R__c); if (R__v) { }
> TDirectory::Streamer(R__b);
> R__b.CheckByteCount(R__s, R__c, QMyDir::IsA());
> } else {
> R__c = R__b.WriteVersion(QMyDir::IsA(), kTRUE);
> TDirectory::Streamer(R__b);
> R__b.SetByteCount(R__c, kTRUE);
> } }
>
> Now how I get the error in CINT:
>
> root [0] TFile file("file.root","recreate")
> root [1] QMyDir* dir=new QMyDir("dir","dir")
> root [2] file.ls()
> TFile** file.root
> TFile* file.root
> QMyDir* dir dir
> KEY: QMyDir dir;1 dir
> root [3] file.Write()
> (Int_t)0
> root [4] file.Close()
> root [5] .q
>
> root [0] TFile file("file.root","read")
> root [1] file.ls()
> TFile** file.root
> TFile* file.root
> KEY: QMyDir dir;1 dir
> root [2] QMyDir *dir=file.Get("dir")
> Error in <TBuffer::ReadVersion>: Could not find the StreamerInfo with
> a checksum of 0 for the class "TUUID" in file.root.
> Error in <TBuffer::CheckByteCount>: object of class TUUID read too few
> bytes: 22 instead of 898023151
> Error in <TBuffer::CheckByteCount>: Byte count probably corrupted
> around buffer position 85:
> 898023151 for a possible maximum of 17
> SysError in <TFile::Seek>: cannot seek to position 60235645022633984
> in file file.root, retpos=-1 (Invalid argument)
> Error in <TFile::ReadBuffer>: error reading all requested bytes from
> file file.root, got 186 of 2687036
>
>
> Thanks!
> Pierre-Luc Drouin
>
>
Received on Mon Mar 17 2008 - 22:08:37 CET