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

From: Pierre-Luc Drouin <pldrouin_at_physics.carleton.ca>
Date: Mon, 17 Mar 2008 16:59:38 -0400

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 - 21:59:57 CET