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Reference Guide
basic.C File Reference

Detailed Description

View in nbviewer Open in SWAN Read data from an ascii file and create a root file with an histogram and an ntuple.

See a variant of this macro in basic2.C.

#include "Riostream.h"
void basic() {
// read file $ROOTSYS/tutorials/tree/basic.dat
// this file has 3 columns of float data
TString dir = gROOT->GetTutorialDir();
dir.Append("/tree/");
dir.ReplaceAll("/./","/");
ifstream in;
in.open(Form("%sbasic.dat",dir.Data()));
Int_t nlines = 0;
auto f = TFile::Open("basic.root","RECREATE");
TH1F h1("h1","x distribution",100,-4,4);
TNtuple ntuple("ntuple","data from ascii file","x:y:z");
while (1) {
in >> x >> y >> z;
if (!in.good()) break;
if (nlines < 5) printf("x=%8f, y=%8f, z=%8f\n",x,y,z);
h1.Fill(x);
ntuple.Fill(x,y,z);
nlines++;
}
printf(" found %d points\n",nlines);
in.close();
f->Write();
}
Author
Rene Brun

Definition in file basic.C.