Read char from txt file in C++

Question

I have a program that will read the number of rows and columns from a txt file. Also, the program has to read the contents of a 2D array from the same file.

Here is the txt file

8 20
 *       
  *
*** 


         ***

8 and 20 are the number of rows and columns respectively. The spaces and asterisks are the contents of the array, Array[8][20] For example, Array[0][1] = '*'

I did make the program reading 8 and 20 as follow:

ifstream myFile;
myFile.open("life.txt");

if(!myFile) {
    cout << endl << "Failed to open file";
    return 1;
}

myFile >> rows >> cols;
myFile.close();

grid = new char*[rows];
for (int i = 0; i < rows; i++) {
    grid[i] = new char[cols];
}

Now, how to assign the spaces and the asterisks to to the fields in the array?

I did the following, but it didn't work

for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            while ( myFile >> ch )
            {
            grid[i][j] = ch;
            }
        }
    }

I hope you got the point.

It would be easier if you replaced whitespaces in the file with, say, dots. — jrok, Sep 07 '12 at 15:22
reading the spaces and asterisks will be before closing the file — Jack in the Box, Sep 07 '12 at 15:23
possible duplicate of [Read int and char from txt file in C++](http://stackoverflow.com/questions/12308299/read-int-and-char-from-txt-file-in-c) — Kerrek SB, Sep 07 '12 at 15:29
@KerrekSB I know that. That post will be deleted soon by the admin. — Jack in the Box, Sep 07 '12 at 15:31
@JackintheBox: Why is the other question being deleted? If there's something wrong with it, you should edit it and fix it. You can ask a moderator to clean out the comments. — Kerrek SB, Sep 07 '12 at 15:36

Alex · Answer 1 · 2012-09-07T15:53:17.047

3

You can do something like this:

for (int y = 0; y < rows; y++) {
    for (int x = 0; x <= cols; x++) {
        char ch = myFile.get();
        if (myFile.fail()) <handle error>;
        if (ch != '\n') grid[y][x] = ch;
    }
}

edited Sep 07 '12 at 15:53

answered Sep 07 '12 at 15:36

Alex

948
1
13
17

something like this is right. Because this definitely bombs the newlines. – Mooing Duck Sep 07 '12 at 17:14

score 0 · Accepted Answer · answered Sep 07 '12 at 18:13

0

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

using namespace std;

int main()
{
    ifstream myFile("file.txt");

    if(!myFile) { 
      cout << endl << "Failed to open file";
        return 1;
    }

    int rows = 0, cols = 0;
    myFile >> rows >> cols;

    vector<vector<char> > grid(rows, vector<char>(cols));
    for(int i = 0;i < rows;i++)
    {
        for(int j = 0;j < cols;j++)
        {
            if(myFile.fail()) {cout << "Improper data in file" << endl;}
            myFile >> grid[i][j];
        }
    }
    myFile.close();

    //Printing the grid back
    std::cout << "This is the grid from file: " << endl;
    for(int i = 0;i < rows;i++)
    {
        cout << "\t";
        for(int j = 0;j < cols;j++)
        {
            cout << grid[i][j];
        }
        cout << endl;
    }
}

answered Sep 07 '12 at 18:13

Jatin Ganhotra

6,825
6
48
71

There is a problem in your code but I don't know where it is... It didn't work.... Thanks though! – Jack in the Box Sep 07 '12 at 19:29
That's not possible. I put it here only when I tested it. Can you tell me what was the problem? – Jatin Ganhotra Sep 08 '12 at 07:56
Do I have to initialize `grid[i][j]` before reading the file? – Jack in the Box Sep 10 '12 at 20:34
http://stackoverflow.com/questions/5222404/c-value-of-uninitialized-vectorint Refer here for your answer. Please accept/upvote the answer if you got it working – Jatin Ganhotra Sep 12 '12 at 07:30

Read char from txt file in C++

2 Answers2