C++ File-stream Vector Input - c++

Question

I am currently working in c++. My goal is to be able to implement the A* algorithm, through a series of steps I plan to be able to store, and list the shortest path from Point A to Point B.
My program will take in a command-line argument which will be a file to read in. The purpose of giving the program a file t read in is that each file is its own "grid" for A* to process. The format for the grid file is as follows:
Num 1 = WIDTH and then Num 2 = HEIGHT
o = start
* = finish
. = passable node
# = impassable wall
So an example grid, let's call it "Grid1", would be:
8 5
o......#
......##
.....###
....####
.......*
So to process this, when you run the program you would pass in "Grid1".
From here, I plan to create a filestream and read in each character into a 2D Array/Vector to attempt to recreate the grid so I can have positions. For example, in "Grid1" the character "o" would be at position [0][0] in a Array/Vector. My attempted implementation is as follows:
#include <iostream>
#include <fstream>
#include <vector>
#include <unordered_map>
using namespace std;
int main(int argc, char *argv[])
{
//Checking for CLA
if( argc < 1 )
{
cout << "Program must take atleast <1> arguments!" << endl << "1) File to read 2) OPTIONAL: Type of search" << endl;
}
//CLA #1 is the file containing GRID to be read in
string gridTBO = argv[1];
//Start new filestream and open grid file for reading
ofstream gridFile;
gridFile.open( gridTBO );
//Check to make sure we can even open the file before proceeding
if( gridFile.is_open() )
{
//To store grid data
vector<string> grid;
grid[0][0].push_back("Hello");
cout << grid[0][0];
}
However, in regards to my "push_back", it seems that I am not able to print out or throw the data into the vector. I would primarily want each index such as [0][0] [0][1] [0][2] to hold each individual character in order to recreate a grid like the one I pass in.
I am not quite sure what I am doing incorrectly as I am fairly inexperienced using vectors, however, the code for pushing data into the grid is purely for testing purposes. Once I am able to parse some data into the vector, I would then like to automate it with a loop and have "getline" or a similar function grab the data for me.
So my main questions are:
1) Why is my push_back and print out failing?
2) How would I read in char by char with a loop to prevent me from manually putting data in?
The error I receive on run-time is:
Segmentation Fault(core dump)
Thank you everyone in advance for your assistance and knowledge!

Answer 1

ofstream is for output file. Use ifstream for reading the file.
vector<string> grid;
vector<string> will work in your case. But it's easier to create a 2-D array of vector with vector<vector<char>>, then you access grid[x][y]
Unlike arrays, vectors don't have any elements when they are created, so there is no valid grid[x][y] or grid[x] until you add something to it.
Try this code instead:
int main()
{
ifstream fin("test.txt");
vector<vector<char>> grid;
int row = 0;
string line;
while(fin >> line)
{
grid.resize(row + 1);
for(auto c : line)
grid[row].push_back(c);
row++;
}
for(auto row_vector : grid)
{
for(auto e : row_vector)
cout << e;
cout << "\n";
}
return 0;
}