Outputting to Text Files

Much like how you can input data from a file, you can also output data to a file. Say you have a matrix and you want to save the results to a text file. You'll see that the code for outputting the matrix to a file looks quite similar to the code for outputting the matrix to the terminal.

You will need to run this code locally in order to see the outputted text file.

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int main() {

    // create the vector that will be outputted
    vector < vector <int> > matrix (5, vector <int> (3, 2));
    vector<int> row;

    // open a file for outputting the matrix
    ofstream outputfile;
    outputfile.open ("matrixoutput.txt");

    // output the matrix to the file
    if (outputfile.is_open()) {
        for (int row = 0; row < matrix.size(); row++) {
            for (int column = 0; column < matrix[row].size(); column++) {
                if (column != matrix[row].size() - 1) {
                    outputfile << matrix[row][column] << ", ";
                }
                else {
                    outputfile << matrix[row][column];
                }
            }
            outputfile << endl; 
        }
    }

    outputfile.close();

    return 0;
}

You can see that you need to create an ofstream object and then use the object to create a new file.

    ofstream outputfile;
    outputfile.open ("matrixoutput.txt");

The rest of the code iterates through the matrix and outputs the matrix in the format you specify in the code:

    if (outputfile.is_open()) {
        for (int row = 0; row < matrix.size(); row++) {
            for (int column = 0; column < matrix[row].size(); column++) {
                if (column != matrix[row].size() - 1) {
                    outputfile << matrix[row][column] << ", ";
                }
                else {
                    outputfile << matrix[row][column];
                }
            }
            outputfile << endl; 
        }
    }

The if statement is checking whether or not the end of the row is reached. If the current value is the end of a row, it's not necessary to put a comma separator after the number:

                if (column != matrix[row].size() - 1) {
                    outputfile << matrix[row][column] << ", ";
                }
                else {
                    outputfile << matrix[row][column];
                }