Question

I’m trying to read some xyz coordinates from an input file.
This is the input file I have:

input.inp

POSITIONS
1.5    2.5    1.5    C
3.2    1.5    4.5    C
1.4    4.2    3.2    C

I want to write a function that searches the input file for the string containing " C" and then starting reading the coordinates from that line. How do I do this in c++? (I don’t want to search for the the word POSITIONS, as that part of the input file may change later).

Answer 1

ifstream file("in");
string line;
while (getline(file, line)) { 
    if (line.find(" C") == string::npos)
        continue;
    istringstream ss(line);
    double x, y, z;
    ss >> x >> y >> z;
    if (!ss)
        continue; // error
    // ok
}