Store a .txt file columns into an array in c++

Question

I am new to programming, so I have what is probably a basic question. I currently have a text file with 2 columns. Each line has x and y numbers separated by white spaces. These are the first five lines of the file:

I want to read the data and store them into x and Y columns and then call for the data some where else in the program for eg x[i] and y[i]. Say, I do not know the number of lines. This is the part of my code where I attempt to do just that.

#include <fstream>
#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
    double X[];
    double Y[];

    ifstream inputFile("input.txt");
    string line;

    while (getline(inputFile, line))
    {
        istringstream ss(line);

        double x,y;

        ss >> x >> y;
        X = X + [x];
        Y = Y + [y];

        return 0;
    }
}

This is a duplicate question, that coincidentally I have already answered in depth. Check it out stackoverflow.com/questions/40307840/… and let me know if it helps, it should. It pertains to the specific problem you are having. — Nick Pavini
– Nick Pavini, Commented Oct 31, 2016 at 18:49
This is a duplicate question, I would recommend reading up on this stackoverflow.com/questions/7868936/read-file-line-by-line it should be easier since you are a beginner and already implements some of the same functionality you have. — I'm here for Winter Hats
– I'm here for Winter Hats, Commented Oct 31, 2016 at 18:53
@user5468794 This is not a duplicate problem because he wants to store into separate containers. — Jonathan Mee
– Jonathan Mee, Commented Oct 31, 2016 at 19:06
Think about using a structure to contain X and Y, then use an std::vector of those structures. If you are really good, you could figure out how to use std::pair and not write a structure. — Thomas Matthews
– Thomas Matthews, Commented Oct 31, 2016 at 19:46
@NickPavini that is not the same thing that was asked in this question. — Adan Vivero
– Adan Vivero, Commented Jan 14, 2022 at 21:25

Raindrop7 · Accepted Answer · 2016-10-31 18:59:38Z

5

the good thing to do is use vector:

vector<double> vecX, vecY;
double x, y;

ifstream inputFile("input.txt");

while (inputFile >> x >> y)
{
    vecX.push_back(x);
    vecY.push_back(y);
}

for(int i(0); i < vecX.size(); i++)
    cout << vecX[i] << ", " << vecY[i] << endl;

answered Oct 31, 2016 at 18:59

Raindrop7

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2 Comments

Abdul Over a year ago

Really helped a lot. Thank you

Jonathan Mee Over a year ago

@Abdul I believe this is your best solution. If it solved your problem please accept it.

sim642 · Accepted Answer · 2016-10-31 18:50:55Z

0

The recommended way would be to use a std::vector<double> or two (one for each column) because values can be easily added to them.

answered Oct 31, 2016 at 18:50

sim642

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