dirs.C File Reference

Detailed Description

This macro illustrates how to create a hierarchy of directories in a Root file.

Ten directories called plane0, plane1, ..., plane9 are created. Each plane directory contains 200 histograms. Note that the macro deletes the TFile object at the end! Connect the file again in read mode:

Root [0] TFile top("top.root");

The hierarchy can be browsed by the Root browser as shown below

Root  TBrowser b;

Click on the left pane on one of the plane directories. This shows the list of all histograms in this directory. Double click on one histogram to draw it (left mouse button). Select different options with the right mouse button. Instead of using the browser, you can also do:

Root > tof->cd();
Root > plane3->cd();
Root > h3_90N->Draw();

void dirs() {
   // create a new Root file
   TFile *top = new TFile("top.root","recreate");

   // create a subdirectory "tof" in this file
   TDirectory *cdtof = top->mkdir("tof");
   cdtof->cd();    // make the "tof" directory the current directory

   // create a new subdirectory for each plane
   const Int_t nplanes = 10;
   const Int_t ncounters = 100;
   char dirname[50];
   char hname[20];
   char htitle[80];
   Int_t i,j,k;
   TDirectory *cdplane[nplanes];
   TH1F *hn[nplanes][ncounters];
   TH1F *hs[nplanes][ncounters];
   for (i=0;i<nplanes;i++) {
      sprintf(dirname,"plane%d",i);
      cdplane[i] = cdtof->mkdir(dirname);
      cdplane[i]->cd();
      // create counter histograms
      for (j=0;j<ncounters;j++) {
         sprintf(hname,"h%d_%dN",i,j);
         sprintf(htitle,"hist for counter:%d in plane:%d North",j,i);
         hn[i][j] = new TH1F(hname,htitle,100,0,100);
         sprintf(hname,"h%d_%dS",i,j);
         sprintf(htitle,"hist for counter:%d in plane:%d South",j,i);
         hs[i][j] = new TH1F(hname,htitle,100,0,100);
      }
      cdtof->cd();    // change current directory to top
   }

   // Fill histograms
   TRandom r;
   for (i=0;i<nplanes;i++) {
      cdplane[i]->cd();
      for (j=0;j<ncounters;j++) {
         for (k=0;k<100;k++) {
            hn[i][j]->Fill(100*r.Rndm(),i+j);
            hs[i][j]->Fill(100*r.Rndm(),i+j+k);
         }
      }
   }

   // save histogram hierarchy in the file
   top->Write();
   delete top;
}

Author

Rene Brun

Definition in file dirs.C.