How to read a map file(0s and 1s) and store it into array in C++?

Question

I want to read a file called maze.txt which contains 0s and 1s (indicated blocked or not), and store every element in the file into 2 dimensionals array called maze[17][17].

maze.txt be like :

11111111111111111
10000000000101001
10100111111001101
10101100001010101
10111010100000001
10000011011111001
11111000010001001
10110010000100101
10110100101110111
10000111000100001
10110011000100101
10110010000011101
10111001111110101
10110010000010001
10010111110101111
10010000000000001
11111111111111111

What I've searched the closest answer is using getline() plus istringstream() (refer to : Read from file in c++ till end of line?)

But above solution only applies when I put a whitespace between each of them, like :

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1
1 0 1 0 0 1 1 1 1 1 1 0 0 1 1 0 1
1 0 1 0 1 1 0 0 0 0 1 0 1 0 1 0 1
1 0 1 1 1 0 1 0 1 0 0 0 0 0 0 0 1
1 0 0 0 0 0 1 1 0 1 1 1 1 1 0 0 1
1 1 1 1 1 0 0 0 0 1 0 0 0 1 0 0 1
1 0 1 1 0 0 1 0 0 0 0 1 0 0 1 0 1
1 0 1 1 0 1 0 0 1 0 1 1 1 0 1 1 1
1 0 0 0 0 1 1 1 0 0 0 1 0 0 0 0 1
1 0 1 1 0 0 1 1 0 0 0 1 0 0 1 0 1
1 0 1 1 0 0 1 0 0 0 0 0 1 1 1 0 1
1 0 1 1 1 0 0 1 1 1 1 1 1 0 1 0 1
1 0 1 1 0 0 1 0 0 0 0 0 1 0 0 0 1
1 0 0 1 0 1 1 1 1 1 0 1 0 1 1 1 1
1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

My code:

void read_maze(int map[17][17]) {
    ifstream read_file("D:/maze.txt", ios::in);
    if (read_file.good()){
        string str;
        int i = 0;
        while (getline(read_file, str) {
            int j = 0;
            istringstream ss(str);
            int num;
            while (ss >> num)
            {
                map[i][j] = num;
                j++;
            }
            i++;
        }
    }
    for (int i = 0; i < 17; i++)
    {
        for (int j = 0; j < 17; j++)
        {
            cout << map[i][j];
        }
        cout << endl;
    }
    read_file.close();
}

output is like original maze.txt

So, what should I do to store each of the element in maze.txt into an array without modifying the content of it?

I believe there might be some easier solutions to it, but since I'm a newbie to C++, I can't find any of similar situations like me.

Hope someone can provide detailed code based on above code. Thanks a lot!

why don't you use char c; and call `read_file >> c;` in a nested loop instead? Then all that remains is to convert c into an integer like `num = c - '0';` — nurettin, Oct 16 '21 at 15:32
Thanks @nurettin , your solution works magically and very clear for me! It seems that what I've worked for hours was solved by you in just a few seconds :) — Learning, Oct 16 '21 at 15:50
actually it was solved 20 years ago, and took several hours. — nurettin, Oct 16 '21 at 16:46

score 0 · Answer 1 · answered Oct 16 '21 at 15:38

You can do it like this :

#include <array>
#include <iostream>
#include <string>
#include <sstream>

std::istringstream file{
    "11111111111111111\n"
    "10000000000101001\n"
    "10100111111001101\n"
    "10101100001010101\n"
    "10111010100000001\n"
    "10000011011111001\n"
    "11111000010001001\n"
    "10110010000100101\n"
    "10110100101110111\n"
    "10000111000100001\n"
    "10110011000100101\n"
    "10110010000011101\n"
    "10111001111110101\n"
    "10110010000010001\n"
    "10010111110101111\n"
    "10010000000000001\n"
    "11111111111111111\n"
};

auto load(std::istream& is)
{
    // use std::array, you can actually return that from functions
    // and avoids the pain of having to work with double pointers
    // and manual memory managment.
    std::array<std::array<char, 17>, 17> map{};

    // loop over all rows in the map
    for (auto& row : map)
    {
        // loop over all the values in a row
        for (auto& value : row)
        {
            // read one value from the file
            is >> value;
        }

        // newlines will be skipped.
    }

    // and return your map (2d array)
    return map;
}

int main()
{
    // file is a stringstream now but
    // is easily replaced by a filestream
    // (stringstream just makes testing more easy)
    auto map = load(file);

    // just another range based for loop
    // to display the map we read from file.
    for (const auto& row : map)
    {
        for (const auto& value : row)
        {
            std::cout << value;
        }
        std::cout << "\n";
    }
}

Thanks @Pepijn Kramer for your answer, but it still seems difficult for a newbie like me! — Learning, Oct 16 '21 at 15:52

Tianshi 25 · Answer 2 · 2021-10-16T15:57:33.200

Your code would work with a slight modification. Like this:

#include <fstream>
#include <iostream>
#include <sstream>

using namespace std;

void read_maze(int map[17][17]) {
    ifstream read_file("maze.txt", ios::in);
    if (read_file.good()){
        string str;
        int i = 0;
        while (getline(read_file, str)) {
            // read line and process each digit
            for (int j=0; j < str.size(); j++) {
                map[i][j] = str[j] - '0';
            }
            i++;
        }
    }
    for (int i = 0; i < 17; i++)
    {
        for (int j = 0; j < 17; j++)
        {
            cout << map[i][j] << " ";
        }
        cout << endl;
    }
    read_file.close();
}

int main() {
    int map[17][17] = {};
    read_maze(map);
}

It's better to explain what was wrong and show the correction than just drop a buch of corrected code. — hivert, Oct 16 '21 at 16:57

How to read a map file(0s and 1s) and store it into array in C++?

2 Answers2