Hello, I'm trying to write a TClonesArray containing one TLorentzVector to a file and read it back. To write the file, I use this function: void write_lv() { TFile tf("test_lv.root","recreate"); TClonesArray clarr("TLorentzVector",5); TLorentzVector* lv = new (clarr[0]) TLorentzVector(); lv->SetPxPyPzE(1,2,3,4); cout << "storing a lorentz vec with a mas of "<<lv->M() << endl; cout << "momentum: ("<<lv->Px()<< ", "<< lv->Py() << ", " << lv->Pz() << " )"<<endl; cout << "array has "<< clarr.GetEntries()<<" entries"<<endl; clarr->Write("an_array"); tf.Close(); } Then I start new root session, open the file, and try to read the TClonesArray: root [0] TFile tf("test_lv.root") root [1] tf.ls() TFile** test_lv.root TFile* test_lv.root KEY: TLorentzVector an_array;1 A four vector with (-,-,-,+) metric root [2] TClonesArray* arr = tf.Get("an_array") root [3] arr->GetEntries() *** Break *** segmentation violation Root > root [4] arr (class TClonesArray*)0x8979720 So I didn't get a null pointer, but using it as a TClonesArray, e.g. by calling GetEntries() on it, doesn't work. Also, from the TFile::ls() output, you could already tell that what has been written is a TLorentzVector, and not a TClonesArray. And indeed I can use the pointer I get from the file if I interpret it as a TLorentzVector: root [7] TLorentzVector* lv2 = tf.Get("an_array") root [8] lv2->M() (const Double_t)1.41421356237309515e+00 This number matches what I expect from what I wrote (sqrt(2)). This is root 3.03/09 on Linux RH6. Does anyone have any idea what is going wrong? Thanks! Paul Balm
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