Reading text file into array character by character, maybe with vectors?

Question

I have a text file that is in the format of a rectangle, with various characters. What I want to do is to read that text file into a 2d array, like a grid. For an example, if the text file was something like this

If I was to call grid[3][2], with [x] and [y] parameters respectively, the value of grid[3][2] would be 5, which is found in row 3, column 2.

I originally tried doing this by declaring the grid as a char array

array[x][y]

Where I had determined the values of x and y (how many lines were in the file, how many columns were in the file) by reading how many lines were in the file, and how many characters were in a line. I know that my code is likely superfluous and I could cut down on the amount of work by implementing a vector array, but I'm not sure how I would go about doing that.

int x = 0; int y = 0;
grid[x][y] = whatever the current character in the file is;
every time a character is stored, x++
when a newline is encountered, y++;

I would think that would properly save all the values to the grid, but I don't know the syntax on how to do that.

Another idea I thought about was to maybe have an array of Points, a class I would create that would contain an X value and a Y value, though I've no idea how I would actually implement it.

I've got no idea about how to go about doing the first option syntax wise, and I've got no clue on how to even start with my second option. Can anyone give me some hints or redirect me to any information that would help teach me?

EDIT: code that crashes

#include <iostream>
#include <fstream>
#include <stdlib.h>
#include <string>
#include <vector>
using namespace std;
std::vector<std::string> grid;
std::string line;
int main(int argc, char** argv)
{
std::string current_exec_name = argv[0];
std::string filename;
if (argc > 1){
    filename = argv[1];
}
cout << filename;
ifstream infile(filename.c_str());
while (infile.good())
{
    grid.push_back(line);
}
grid[2][1] = 4;
//the line above

}

I've tried doing the following codes where the program crashes

grid[2][1] = 4;
grid[2][1] = "4";
grid[2] = 4;
grid[2] = "4";

The program builds, but crashes when it runs.

grid[3][2] should actually return 4 (assuming we start counting the indices from 0). Right? — David G
– David G, Commented Nov 24, 2013 at 21:49

David G · Accepted Answer · 2013-11-24 21:50:55Z

3

You can use a vector of strings to insert each line into:

std::vector<std::string> grid;
std::string line;

while (std::getline(in, line))
{
    grid.push_back(line);
}

Now by accessing the [x][y] points you will get the correct character in the file:

grid[3][2]; // 4

answered Nov 24, 2013 at 21:50

David G

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6 Comments

JC2112 Over a year ago

Actually, I'm trying to as a test, (after implementing the above code), declare that grid[3][2] = 4, and then cout grid[3][4], but the program crashes. It builds right, but it crashes. Was I supposed to do a different declaration of grid, the first line in the code you gave me?

David G Over a year ago

@JoJoBya Can you show me your actual code that crashes? Maybe I can help.

David G Over a year ago

@JoJoBya I think I see the problem. You're doing while (infile.good()) when you should be doing while (std::getline(infile, line)). Sorry I took so long to reply, I had to help my mom with something.

JC2112 Over a year ago

Well, replacing while (infile.good()) with while (std::getline(infile, line)) makes it give me an error of "no matching function for call to 'getline'

JC2112 Over a year ago

let us continue this discussion in chat

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