[examples] Macro demonstrates reading a star generator event file (#506)

Demonstrates how to read one of the event generator record files, load an event, and iterate over all particles.

StRoot/StarGenerator/macros/starsim.reader.standalone.C

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+/**!
+ * Example macro for running an event generator in standalone mode.
+ *
+ * Usage:
+ *
+ * ln -s starsim.reader.C reader.C
+ *
+ * root4star
+ * .L reader.C
+ * int nevents=100;
+ * reader( nevents )
+ *
+ * or
+ *
+ * root4star -q -b reader.C 
+ *
+ */
+
+class St_geant_Maker;
+St_geant_Maker *geant_maker = 0;
+
+class StarGenEvent;
+StarGenEvent   *event       = 0;
+
+class StarPrimaryMaker;
+StarPrimaryMaker *_primary = 0;
+
+class StarGenEventReader;
+StarGenEventReader *eventreader = 0;
+
+
+// ----------------------------------------------------------------------------
+// ----------------------------------------------------------------------------
+// ----------------------------------------------------------------------------
+void reader( Int_t nevents=1, UInt_t rngSeed = 12345 )
+{ 
+
+  gROOT->ProcessLine(".L bfc.C");
+  {
+    TString simple = "tables nodefault";
+    bfc(0, simple );
+  }
+
+  gSystem->Load( "libVMC.so");
+  gSystem->Load( "St_g2t.so" );
+  gSystem->Load( "St_geant_Maker.so" );
+
+  gSystem->Load( "StarGeneratorUtil.so" );
+  gSystem->Load( "StarGeneratorEvent.so" );
+  gSystem->Load( "StarGeneratorBase.so" );
+
+  gSystem->Load( "libMathMore.so"   );  
+  gSystem->Load( "libStarGenEventReader.so" );
+
+
+  eventreader = new StarGenEventReader();
+  eventreader -> SetInputFile("pythia_jet_vz0_run1.genevent.root","genevents","primaryEvent");
+
+
+  chain->Clear();
+  chain->Make();
+
+  StarGenEvent* event = eventreader->Event();
+
+
+  std::cout << "GENERATOR ID  = " << event->GetGeneratorId() << std::endl;
+  std::cout << "PROCESS ID    = " << event->GetProcessId() << std::endl;
+  std::cout << "RUN NUMBER    = " << event->GetRunNumber() << std::endl;
+  std::cout << "EVENT NUMBER  = " << event->GetEventNumber() << std::endl;
+  std::cout << "NUM PARTICLES = " << event->GetNumberOfParticles() << std::endl;
+
+  StarGenParticle* particle;
+  TIter& Next = event->IterAll();
+  while( (particle = (StarGenParticle*)Next() ) ) {
+    particle->Print();
+  }
+
+
+
+
+}
+// ----------------------------------------------------------------------------
+