C++ 读入第一项，检查，然后读入 rest 项

Question

I have a file that looks like this:

# Some comments
Some data

Each line in the data section will have 5 items.

I would like to read in the file, line by line, but ignore the comments. To do this, I think I would need to check if the first item is a # . However, when I run the code below, I get a segmentation fault:

void readFile(string f, unordered_map<int, vector<double>> &l1, unordered_map<int, vector<double>> &l2,
              unordered_map<int, vector<double>> &l3) {
    ifstream          file(f);
    string first;
    int second;
    float third, fourth, fifth;

    string line;

    while(getline(file, line))
    {
        std::stringstream  lineStream(line);
        // Read an integer at a time from the line
        lineStream >> first;
        if (first == "#") { continue;}
        else {
            lineStream >> second >> third >> fourth >> fifth;
            vector<double> location {third, fourth, fifth};
            if (first == "sat") { l1[second].insert(l1[second].end(), location.begin(), location.end());
            } else if (first == "user") {l2[second].insert(l2[second].end(), location.begin(), location.end());
            } else {l3[second].insert(l3[second].end(), location.begin(), location.end());
            }
            cout << second << " " << third << " " << fourth << " " << fifth;
        }
    }

Does anyone know why?

Answer 1

You have lineStream delcared as a stringstream. To use the extraction operator you need to declare it as an istringstream so you can read from it.

Change

std::stringstream lineStream(line);

to

std::istringstream lineStream(line);