ROOT CERN指针类型不匹配求助：无法从ROOT文件生成直方图

初始错误信息 #

Error in TTree::SetBranchAddress: The pointer type given "Double_t" (8) does not correspond to the type needed "vector" by the branch: mu_phi

运行脚本后画布仅显示条目数、均值等统计信息，所有直方图样式完全一致。尝试将Double_t替换为vector<float>后，出现新编译错误：

error: no matching member function for call to 'Fill'
muEta->Fill(mu_eta);

/snap/root-framework/838/usr/local/include/TH1.h:219:21: note: candidate function not viable: no known conversion from 'vector<float>' to 'Double_t' (aka 'double') for 1st argument
 virtual Int_t    Fill(Double_t x);
                  ^
/snap/root-framework/838/usr/local/include/TH1.h:220:21: note: candidate function not viable: requires 2 arguments, but 1 was provided
 virtual Int_t    Fill(Double_t x, Double_t w);
                  ^
/snap/root-framework/838/usr/local/include/TH1.h:221:21: note: candidate function not viable: requires 2 arguments, but 1 was provided
 virtual Int_t    Fill(const char *name, Double_t w);

原始脚本 #

void script(){
  
  TFile *file = TFile::Open("output_data.root");

  TTree* tree = (TTree*)file->Get("nominal");

  TChain* fchain = new TChain("nominal");
  fchain->Add("output_data.root");
                                                            
  Double_t mu_pt, mu_e, mu_eta, mu_phi;

   //set branches to variables
  tree->SetBranchAddress("mu_pt", &mu_pt);
  tree->SetBranchAddress("mu_e", &mu_e);
  tree->SetBranchAddress("mu_eta", &mu_eta);
  tree->SetBranchAddress("mu_phi", &mu_phi);

  TH1D *muPt = new TH1D("muPt", ";p_{T} [GeV/c];Events", 100, 0., 200.);
  TH1D *muEta = new TH1D("muEta", ";;#eta;Events", 50, -3, 3);
  TH1D *muE = new TH1D("muE", ";;Energy;Events", 50, 0, 200);
  TH1D *muPhi = new TH1D("muPhi", ";;#phi;Events", 50, -4, 4);
  TH1D *mass = new TH1D("mass", ";;mass;Events", 50, 0, 200);

  Long64_t nentries = fchain->GetEntries();

  for (int i=0; i<nentries ; i++) {

  Long64_t ientry = fchain->LoadTree(i);
  if (ientry <0 ) break;

  fchain->GetEntry(i);

  muEta->Fill(mu_eta);
  muPt->Fill(mu_pt);
  muPhi->Fill(mu_phi);
  muE->Fill(mu_e);
}
   cout << "entries = " << nentries << endl;

   TCanvas *c1 = new TCanvas("Eta","Eta",800 ,800);
   c1->cd();
   muEta->Draw();

}

ROOT版本：6.26/10

解决方案 #

1. 正确绑定vector类型分支 #

分支mu_pt、mu_e、mu_eta、mu_phi均为vector<float>类型，需将变量声明为对应类型，同时删除冗余的TFile和TTree代码（直接用TChain即可）：

#include <vector> // 必须包含vector头文件

vector<float> mu_pt, mu_e, mu_eta, mu_phi;

// 绑定分支地址到vector变量
fchain->SetBranchAddress("mu_pt", &mu_pt);
fchain->SetBranchAddress("mu_e", &mu_e);
fchain->SetBranchAddress("mu_eta", &mu_eta);
fchain->SetBranchAddress("mu_phi", &mu_phi);

2. 遍历vector填充直方图 #

TH1D::Fill()仅接受单个数值，需遍历vector中的每个元素完成填充（假设每个事件的四个vector长度一致，对应同一批粒子的属性）：

for (int i=0; i<nentries ; i++) {
    Long64_t ientry = fchain->LoadTree(i);
    if (ientry <0 ) break;

    fchain->GetEntry(i);

    // 遍历每个粒子的属性填充直方图
    for (size_t j=0; j<mu_eta.size(); j++) {
        muEta->Fill(mu_eta[j]);
        muPt->Fill(mu_pt[j]);
        muPhi->Fill(mu_phi[j]);
        muE->Fill(mu_e[j]);
    }
}

3. 修正后的完整脚本 #

#include <vector>
#include <iostream>
using namespace std;

void script(){
  // 直接用TChain处理文件，无需额外TFile
  TChain* fchain = new TChain("nominal");
  fchain->Add("output_data.root");
                                                            
  // 声明vector类型变量
  vector<float> mu_pt, mu_e, mu_eta, mu_phi;

  // 绑定分支地址到vector变量
  fchain->SetBranchAddress("mu_pt", &mu_pt);
  fchain->SetBranchAddress("mu_e", &mu_e);
  fchain->SetBranchAddress("mu_eta", &mu_eta);
  fchain->SetBranchAddress("mu_phi", &mu_phi);

  // 创建直方图，修正标题格式
  TH1D *muPt = new TH1D("muPt", ";p_{T} [GeV/c];Events", 100, 0., 200.);
  TH1D *muEta = new TH1D("muEta", ";#eta;Events", 50, -3, 3);
  TH1D *muE = new TH1D("muE", ";Energy [GeV];Events", 50, 0, 200);
  TH1D *muPhi = new TH1D("muPhi", ";#phi;Events", 50, -4, 4);

  Long64_t nentries = fchain->GetEntries();
  cout << "Total entries: " << nentries << endl;

  for (int i=0; i<nentries ; i++) {
    Long64_t ientry = fchain->LoadTree(i);
    if (ientry <0 ) break;

    fchain->GetEntry(i);

    // 遍历每个粒子的属性填充直方图
    for (size_t j=0; j<mu_eta.size(); j++) {
      muEta->Fill(mu_eta[j]);
      muPt->Fill(mu_pt[j]);
      muPhi->Fill(mu_phi[j]);
      muE->Fill(mu_e[j]);
    }
  }

  // 绘制并设置直方图样式
  TCanvas *c1 = new TCanvas("Eta","Eta",800 ,800);
  c1->cd();
  muEta->SetLineColor(kBlue); // 设置线条颜色区分样式
  muEta->Draw();
  c1->SaveAs("mu_eta_hist.pdf"); // 可选保存为文件

  // 绘制其他直方图
  TCanvas *c2 = new TCanvas("Pt","Pt",800 ,800);
  c2->cd();
  muPt->SetLineColor(kRed);
  muPt->Draw();
  c2->SaveAs("mu_pt_hist.pdf");
}

关键说明 #

• 必须包含<vector>头文件，否则无法识别vector类型
• 每个事件可能包含多个粒子，vector存储了同一事件内所有粒子的对应属性，需遍历填充
• 可通过SetLineColor等方法设置直方图样式，避免所有图外观一致
• TChain支持添加多个ROOT文件，后续扩展只需调用fchain->Add("xxx.root")

内容的提问来源于stack exchange，提问作者arrakis