C++ reading from a text file into a array/string

Question

Here is the code I have so far.

What I need to do is read from two different text files, Matrix A and Matrix B.

I can do this however for each text file matrix I read it only comes up with

1 0 0

(so basically the first line) where the whole text file for Matrix A is in fact

1 0 0
2 0 0
3 0 0

so does anybody know how I can do this?

Thanks!

#include <iostream>  //declaring variables
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;
string code(string& line);
int main()
{
    ofstream outf;
    ifstream myfile;
    string infile;
    string line;
    string outfile;

    cout << "Please enter an input file (A.txt) for Matrix A or (B.txt) for Matrix B" << endl;
    cin >> infile;   //prompts user for input file

    if (infile == "A.txt")
    {      //read whats in it and write to screen
        myfile.open("A.txt");
        cout << endl;
        getline (myfile, line);
        cout << line << endl;

    }
    else
        if (infile == "B.txt")
        {
            myfile.open("B.txt");
            cout << endl;
            getline (myfile, line);
            cout << line << endl;
        }
        else
    { 
        cout << "Unable to open file." << endl;
    }
        //{
            //while("Choose next operation");
        //}
    return 0;
}

Eutherpy · Accepted Answer · 2014-04-19 16:08:41Z

9

Well, getline obviously gets one line.

You should read line by line until the end of file, and you can achieve that with, for example:

while (getline(myfile, line))
    out << line << endl;

This means: while there is a line to get from myfile, write that line to the output stream.

edited Apr 19, 2014 at 16:08

answered Apr 19, 2014 at 16:01

Eutherpy

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Comments

László Papp · Accepted Answer · 2014-04-19 15:59:46Z

2

You are reading only once, so this is not a miracle. You will need to use a while or for loop for continous reading. You would be writing something like this:

while (getline (myfile, line))
    cout << line << endl;

This would be the whole code to write:

#include <iostream>  //declaring variables
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;
string code(string& line);
int main()
{
    ofstream outf;
    ifstream myfile;
    string infile;
    string line;
    string outfile;

    cout << "Please enter an input file (A.txt) for Matrix A or (B.txt) for Matrix B" << endl;
    cin >> infile;   //prompts user for input file

    if (infile == "A.txt")
    {      //read whats in it and write to screen
        myfile.open("A.txt");
        cout << endl;
        while (getline (myfile, line))
            cout << line << endl;


    }
    else
        if (infile == "B.txt")
        {
            myfile.open("B.txt");
            cout << endl;
            while (getline (myfile, line))
                cout << line << endl;
        }
        else
    { 
        cout << "Unable to open file." << endl;
    }
        //{
            //while("Choose next operation");
        //}
    return 0;
}

answered Apr 19, 2014 at 15:59

László Papp

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2 Comments

user3536870 Over a year ago

I'm literally a beginner to this and struggling a lot so that doesn't mean a great deal to my little knowledge unfortunately. It would help a lot more if you could possibly show me how I could modify my code?

László Papp Over a year ago

@user3536870: cheers, but please get a C++ book, e.g. Bjarne's. Also, please read this.

madx · Accepted Answer · 2015-02-05 12:34:42Z

0

Using getline is the easiest way:

#include <string>
#include <iostream>
#include <fstream>
using namespace std;

void read_file_line_by_line(){
    ifstream file;
    string line;
    file.open("path_to_file");
    while (getline (file, line))
        cout << line << endl;
}

int main(){
    read_file_line_by_line();
    return 0;
}

answered Feb 5, 2015 at 12:34

madx

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