count_events.C

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/*
    BM@N alignment routine
    BM@N experiment at NICA complex, JINR, 2025
 
    Department: Math & Soft Group of HEP lab
    Author:     Igor Polev, polev@jinr.int
 
    Count number of events in a ROOT file
*/
 
// headers below are for IDE syntax to work and they will be
// turned off during execution in ROOT macro mode
#ifndef __CLING__
#include "TCollection.h"
#include "TFile.h"
#include "TKey.h"
#include "TObject.h"
#include "TTree.h"
#endif
 
void count_events(const char* filename)
{
    TFile* f = TFile::Open(filename, "READ");
    if (!f || f->IsZombie()) {
        printf("0\n");
        return;
    }
    TIter next(f->GetListOfKeys());
    TKey* key;
    while ((key = (TKey*)next())) {
        TObject* obj = key->ReadObj();
        if (obj && obj->InheritsFrom(TTree::Class())) {
            // print out the answer
            printf("%lld\n", ((TTree*)obj)->GetEntries());
            f->Close();
            return;
        }
    }
    printf("0\n");
    f->Close();
}