为什么此循环不会加载正确的事件？

Why won't this loop load the proper event?

本文关键字：事件 加载 循环 为什么      更新时间：2023-10-16

这是我写的代码，它运行良好，但它似乎并没有实际加载事件…相反，它似乎用一个任意的小数字填充了直方图和计数。

include "TTree.h"
include "TFile.h"
include "TRandom.h"
include "TTree.h"
include "TCanvas.h"
include "TStyle.h"
include <iostream>
include "TH1.h"
include "TChain.h"
using namespace std;
void readtestsimple(){
  TFile *file = TFile::Open("/file/");
  TTree* comp_tree = (TTree*)file->Get("_compress_tree");
  TChain* compchain = new TChain("_compress_tree");
  compchain->Add("/file/");
  TH1D *comp = new TH1D("comp","_compression",100,0,0.05);
  Double_t _compression, _compressionU, _compressionV, _compressionY, _ch_compression;
  Int_t _ch;
  comp_tree->SetBranchAddress("_compression",&_compression);
  comp_tree->SetBranchAddress("_compressionU",&_compressionU);
  comp_tree->SetBranchAddress("_compressionV",&_compressionV);
  comp_tree->SetBranchAddress("_compressionY",&_compressionY);
      Long64_t nentries = compchain->GetEntries();
      Long64_t nb = 0, nbytes = 0 ;
      for (Long64_t i=0; i<nentries; i++) {
              Long64_t entry = compchain->LoadTree(i);
              if (entry <0 ) break;
             nb = compchain->GetEntry(i); nbytes += nb;
              cout << "entry = " << nb << endl;
              cout << "compression = " << _compression << endl;
              comp->Fill(_compression);
      }
   cout << "entries = " << nentries << endl;
}

我得到的输出是这个的长重复:

entry = 36
compression = 1.54768e-316
entry = 36
compression = 1.54768e-316
entry = 36
compression = 1.54768e-316

(最后是正确的条目数)。

我怎么做才能使它读出正确的条目?请帮助!

看起来你根本不需要使用comp_tree指针。compchain指针应该足以访问TTree中的数据，因为TChain是TTree。因此，您应该能够将变量"链接"到链/树分支，如:

compchain->SetBranchAddress("_compression",&_compression);
不是

comp_tree->SetBranchAddress("_compression",&_compression);
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