TTreeReader and TTreeReaderValue

[forever]

I want to know the “TTreeReaderArray<Char_t> name(myReader_coin_30,“name_Si”);” size, but don’t know what method to use。Can anyone help me with this problem, I will be very grateful to him。

[eguiraud]

Hi @forever ,
and welcome to the ROOT forum. TTreeReaderArray has a GetSize method, see the docs (you have to expand the list of public methods inherited from TTreeReaderArrayBase).

Cheers,
Enrico

[forever]

I use the method that you said,but the terminal show the message “segmentation violation” The code show as below.
TTreeReaderArray<Double_t> N_Erg(myReader_coin_30,“N_Erg”);
cout << "N_Erg.GetSize(): "<<N_Erg.GetSize()<< endl;

[eguiraud]

A segmentation violation is usually due to a bug in the code. It could be anything really. ROOT should print a stacktrace that points to where the segfault happens, if so please paste it here, it might be enough to tell what’s going on.

If that does not help, please share a minimal self-contained reproducer that we can run and debug.
Cheers,
Enrico

[forever]

#include "TFile.h"
#include "TH1F.h"
#include "TTreeReader.h"
#include "TTreeReaderValue.h"
#include "TTreeReaderArray.h"
#include "math.h"
# include <string>
#include "TH1D.h"
#include "TH2D.h"
#include "Riostream.h"
#include "TGraph.h"
#include "TGraphErrors.h"

void plot()
{
//TH2D* Coin_Si_CLLB = new TH2D("Coin_Si_CLLB","Coin_Si_CLLB_45",6400,0.,160.,800,0.,20.);
TCanvas* c = new TCanvas();
TPad *pad1 = new TPad("pad1","pad1",0.03,0.62,0.98,0.92,32);
TPad *pad2 = new TPad("pad2","pad1",0.03,0.02,0.98,0.60,33);
pad1 -> Draw();pad2 -> Draw();
TH1F* h1 = new TH1F("h1","N_Erg",1000,0.,500.);
auto myFile = TFile::Open("result.root");
if (!myFile || myFile->IsZombie()) {
return;
}
TTreeReader myReader_coin_30("tree5", myFile);
TTreeReaderArray<Double_t> N_Erg(myReader_coin_30,"N_Erg");
cout << "N_Erg.GetSize(): "<<N_Erg.GetSize()<< endl;
while (myReader_coin_30.Next())
{
h1 -> Fill(N_Erg[0]);
}
pad1 -> cd();
pad1 -> SetLogy();
h1 -> GetXaxis() -> SetRangeUser(0,500);
h1 -> Draw();
//------------------------
ifstream input;
input.open("./Erg.txt");
if(!input)
{
cout << "do not open the file!" << endl;
return;
}
double x[306];
double y[306];
double a =0;
for(int i = 0; i < 306; i++)
{
input >> x[i] >> y[i];
a = a + y[i]/40.8173;
}
TGraph *gr = new TGraph(306,x,y);
gr -> SetLineColor(kRed);
pad2 -> cd();
pad2 -> SetLogy();
gr -> GetXaxis() -> SetRangeUser(0,500);
gr -> Draw();
}

This is my code,I really do not know how to solve this problem,please help me! Thank you very much!

[eguiraud]

Hi,
we can’t run and debug the code without the input data.

Cheers,
Enrico