2.1. Data Access

In order to access the data we just created a FairRunAna object has to be initialized with the output from the previous steps. This is done in the following lines

// *** the files coming from the simulation
TString inPidFile = "signal_pid.root"; // this file contains the PndPidCandidates and McTruth
TString inParFile = "signal_par.root";

// *** PID table with selection thresholds; can be modified by the user
TString pidParFile = TString(gSystem->Getenv("VMCWORKDIR")) + "/macro/params/all.par";

// *** initialization
FairLogger::GetLogger()->SetLogToFile(kFALSE);
FairRunAna *fRun = new FairRunAna();
FairRuntimeDb *rtdb = fRun->GetRuntimeDb();
fRun->SetSource(new FairFileSource(inPidFile));

// *** setup parameter database
FairParRootFileIo *parIO = new FairParRootFileIo();
parIO->open(inParFile);
FairParAsciiFileIo *parIOPid = new FairParAsciiFileIo();
parIOPid->open(pidParFile.Data(), "in");

rtdb->setFirstInput(parIO);
rtdb->setSecondInput(parIOPid);
rtdb->setOutput(parIO);

fRun->SetSink(new FairRootFileSink("out_dummy.root")); // we create our own output .root file later, so we put here a dummy
fRun->Init();

In order to actually loop through the events one needs an object PndAnalysis

PndAnalysis* theAnalysis = new PndAnalysis ();

which provides some nice functionality to access the data, inluding PID selection. You do not need to take care at all about fetching objects from the input files, since all this is done be the FairRootManager through FairRunAna internally.

The actual event loop itself then looks like

while ( theAnalysis->GetEvent() )
{
  ...
  // here your analysis code goes ...
  ...
}