=========== read_textdata_string_direct.C============
void read_textdata_string_direct(){
  string line;
  vector<string> s;


  cout<<"------------input lines--------------------"<<endl;
  ifstream fin0("tree_input.txt");
  while(getline(fin0,line)) cout<<line<<endl;
  cout<<"------------end of input lines-------------"<<endl;

  ifstream fin("tree_input.txt");
  while(getline(fin,line)) s.push_back(line);

  for(auto x: s) {
    vector<string> ss;
    int c;
    while((c = x.find_first_of(" ")) != string::npos){
      if(c>0) ss.push_back(x.substr(0,c));
      for (int i=c;i>=0;i--) x.erase(i,1);
    }
    ss.push_back(x);
    if(ss[0].empty()) continue;  // skip empty line
    for(auto y:ss) cout<<y<<"\t";
    cout<<endl;
    cout<<"ss[0]="<<ss[0]<<" ss[1]="<<ss[1]<<" ss[2]="<<ss[2]<<endl;
  }
  return;
}

------------input lines--------------------
20  222.98  2021-01-01
 30  555.42  2022-01-13
40  455.12  2022-01-14

 50  355.1
 60  255.2  2022-01-16  45.9
 70  155.4  2022-01-17
80  955.999  2022-01-18




------------end of input lines-------------
20      222.98  2021-01-01
ss[0]=20 ss[1]=222.98 ss[2]=2021-01-01
30      555.42  2022-01-13
ss[0]=30 ss[1]=555.42 ss[2]=2022-01-13
40      455.12  2022-01-14
ss[0]=40 ss[1]=455.12 ss[2]=2022-01-14
50      355.1
ss[0]=50 ss[1]=355.1 ss[2]=
60      255.2   2022-01-16      45.9
ss[0]=60 ss[1]=255.2 ss[2]=2022-01-16
70      155.4   2022-01-17
ss[0]=70 ss[1]=155.4 ss[2]=2022-01-17
80      955.999 2022-01-18
ss[0]=80 ss[1]=955.999 ss[2]=2022-01-18