c++ ifstream end of line

Question

I have a file that looks like this:

e r g d g d
f h d r h f
..........

And I want to store these characters in a two-dimensional array

#include <fstream>
#include <iostream>
using namespace std;
int main()
{
    ifstream file("file.txt");
    char c[20][20];
    int i = 0, j = 0;
    while(!file.eof())
    {
        while(!end of line?)
        {
            file >> c[i][j];
            j++;
        }
        i++;
    }
.....
}

how do i do this?
or how to find number of characters in a line?

why do you use a `char[20][20]` when each line contains only 6 characters? — 463035818_is_not_a_number, Nov 09 '16 at 20:40
if your question is how to know if you reached the end of the line, then the answer is a) you dont have to care, just continue reading, or b) when you read 6 numbers you reached the end of the line :P — 463035818_is_not_a_number, Nov 09 '16 at 20:42
what if there is more than 6 characters in the line, i gave an example — jeff, Nov 09 '16 at 20:43
you just said that the number of characters per line is always the same.... — 463035818_is_not_a_number, Nov 09 '16 at 20:43
@πάντα ῥεῖ the question is about end of line, not about end of file. So even if OPs code has wrong usage of `eof` it is not a duplicate — 463035818_is_not_a_number, Nov 09 '16 at 20:45
why not getline(file, variable), that goes one line at a time, and have that variable be a string, then parse it out and store into the array you want. — Omid CompSCI, Nov 09 '16 at 20:52
Each line has the same number of characters, which is not always 6, the file i included was an example — jeff, Nov 09 '16 at 20:53
you dont need any parsing, just read whatever number of characters you have per line and then continue with the next line. For `cin` it doesnt matter if the characters are seperated by a space or a new line — 463035818_is_not_a_number, Nov 09 '16 at 20:55
that would be easy, the question is how to find the number of characters in a line — jeff, Nov 09 '16 at 20:58
@jeff Like I said, when you use getline and store into a string, before you read the new line again, do stringVariable.length(), and you will know how many characters were on that line. — Omid CompSCI, Nov 09 '16 at 21:03

score 0 · Accepted Answer · edited Nov 10 '16 at 12:39

You can't use eof() like you do. You have to perform an I/O read operation before you can then use eof().

For what you are attempting, you should use std::getline() instead, eg:

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

int main()
{
    std::ifstream file("file.txt");
    std::string line;
    char c[20][20] = {};

    for (int i = 0; i < 20; ++i)
    {
        if (!std::getline(file, line))
            break;

        std::istringstream iss(line);
        for(j = 0; j < 20; ++j)
        {
            if (!(iss >> c[i][j]))
                break;
        }
    }

    ...

    return 0;
}

That being said, you should consider using std::vector instead of fixed-sized arrays (unless you know for a fact that your file will never exceed 20 lines and/or 20 characters per line):

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <iterator>
#include <algorithm>
#include <vector>

int main()
{
    std::ifstream file("file.txt");
    std::vector<std::vector<char> > c;
    std::string line;

    while (std::getline(file, line))
    {
        std::istringstream iss(line);
        std::vector<char> tmp;

        std::copy(
            std::istream_iterator<char>(iss),
            std::istream_iterator<char>(),
            std::back_inserter(tmp)
        );

        /* which is equivalent to:
        char ch;
        while (iss >> ch) {
            tmp.push_back(ch);
        }
        */

        c.push_back(tmp);
    }

    ...

    return 0;
}

Alternatively:

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <iterator>
#include <algorithm>
#include <vector>

typedef std::vector<char> CharVector;

std::istream& operator>>(std::istream &in, CharVector &out)
{
    out.clear();

    std::string line;
    if (std::getline(in, line))
    {
        std::istringstream iss(line);

        std::copy(
            std::istream_iterator<char>(iss),
            std::istream_iterator<char>(),
            std::back_inserter(out)
        );

        /* which is equivalent to:
        char ch;
        while (iss >> ch) {
            out.push_back(ch);
        }
        */
    }

    return in;
}

int main()
{
    std::ifstream file("file.txt");
    std::vector<CharVector> c;

    std::copy(
        std::istream_iterator<CharVector>(file),
        std::istream_iterator<CharVector>(),
        std::back_inserter(c)
    );

    /* which is equivalent to:
    CharVector cv;
    while (file >> cv) {
        c.push_back(cv);
    }
    */

    ...

    return 0;
}

c++ ifstream end of line

1 Answers1