=========== read_textdata_string.C============
vector<string> split_string(string x);

void read_textdata_string(){
  string line;
  ifstream fin("tree_input.txt");
  vector<string> s;
  while(getline(fin,line)) s.push_back(line);

  vector<string> ss;
  for(auto x: s) {
    ss = split_string(x);
    if(ss[0].empty()) continue;
    for(auto y:ss) cout<<y<<"\t";
    cout<<endl;
    cout<<"2nd string = "<<ss[1]<<endl;
}
  return;
}

vector<string> split_string(string x){
    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);
  return ss;
}


=
============== tree_input.txt===============
20  222.  2021-01-01
 30  555.  2022-01-13
40  455.  2022-01-14

 50  355.
 60  255.  2022-01-16  45.9
 70  155.  2022-01-17
80  955.  2022-01-18


===========================================

Processing read_textdata_string.C...
20      222.    2021-01-01
2nd string = 222.
30      555.    2022-01-13
2nd string = 555.
40      455.    2022-01-14
2nd string = 455.
50      355.
2nd string = 355.
60      255.    2022-01-16      45.9
2nd string = 255.
70      155.    2022-01-17
2nd string = 155.
80      955.    2022-01-18
2nd string = 955.