C++: Trying to read from a file line by line, saving into a vector and then printing the vector prints nothing

Question

I am trying to read from a file and insert the data into a vector. The file looks like:

I want my vector to look something like:

16 0 1 0 0 0 1 1 1 0 1 1 1...

My code looks like this:

void readFile(string name){
    ifstream fin;
    vector<int> graphData;
    int y;
    fin.open(name);
    if (!fin.is_open()){
        cout << "Error: Could not open data.";

    }
    else{
        while(!fin.eof()){
            fin >> y;
            graphData.push_back(y);
        }

    }
    fin.close();
    for(int i = 0; i < graphData.size(); ++i){
        cout << graphData[i] << " ";
    }
}

I am pretty sure the issue is with me defining y and then trying to push that in. But when I run the code nothing is outputted like the vector is empty.

Not related to the question: In such cases use try and catch, it'll always help — pasha, Aug 05 '17 at 19:04
check this: https://stackoverflow.com/questions/24094834/how-to-fill-vectors-by-reading-a-file?rq=1 — pasha, Aug 05 '17 at 19:10
Also the output would be: "16 0100 0111 ..." not as you specified — pasha, Aug 05 '17 at 19:14
Can I get it where the output would be 16 0 1 0 0 0 1 1 1 0 1 1 1... I want each number to be in its own index — K22, Aug 05 '17 at 19:23
I think @Thomas Matthews already provided an answer for that, you can go ahead and mark that answer as accepted. — pasha, Aug 05 '17 at 19:25

score 1 · Answer 1 · answered Aug 05 '17 at 19:21

Try reading the numbers as character strings:

unsigned int quantity = 0;
fin >> quantity;
fin.ignore(100000, '\n');
std::string number_text;
vector<int> binary;
while (getline(fin, number_text))
{
  for (int i = 0; i < number_text.length())
  {
    int bit = number_text[i] - '0';
    binary.push_back(bit);
  }
}

score 1 · Accepted Answer · answered Aug 05 '17 at 19:42

1

You could - after skipping the line count - read in each individual character and compare it to '0' or '1'. See the following code:

int main() {

    vector<bool> bits;
    ifstream f(DATAFILE);
    if (f.is_open()) {
        int dummy;
        f >> dummy;
        char c;
        while (f >> c) {
            if (c == '1') {
                bits.push_back(true);
            }
            else if (c=='0') {
                bits.push_back(false);
            }
        }
        f.close();
        for(int i = 0; i < bits.size(); ++i){
            cout << bits[i] << " ";
        }
    }
    return 0;
}

answered Aug 05 '17 at 19:42

Stephan Lechner

34,891
4
35
58

this works great for me. I think I can go from here to continue on with what I am doing. Thank you for your help – K22 Aug 05 '17 at 19:59
You are welcome; please be so kind to accept the answer if it solved your problem. – Stephan Lechner Aug 05 '17 at 20:44

score 0 · Answer 3 · answered Aug 05 '17 at 19:18

0

You should use getline function to get input line by line: After fin.open(name);

do this:

getline(fin,line);

and then save the line to your y

answered Aug 05 '17 at 19:18

pasha

2,035
20
34

Another example: https://stackoverflow.com/questions/7868936/read-file-line-by-line – pasha Aug 05 '17 at 19:19

C++: Trying to read from a file line by line, saving into a vector and then printing the vector prints nothing

3 Answers3