can't print 2d array - file input

Question

maybe this is a very easy question but I'm confused

If my code is named example.c and takes as an input a txt file, lets say txt.txt . I run the command ./example txt.txt in a terminal (linux). According to what the user gives me through the file, I create a 2D array. If the context of the fie is:

+X..XX....-
.X..X..X-..
.X.........
...XX......
XXX.+X.....
..X.....XXX
...XXX..X-.
.-.....X...

I count the lines (in this example 1) and the elements before the new line, to find the rows of my array.

Can you please tell me what I do wrong in the printing of the file into a 2d array?

I can't print the array properly.

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv){
    int lines=0, rows=0, j, k;
    char ch, array[1000][1000];
    FILE *fin;

    if(argc!=2){
        exit(2);
    }

    fin=fopen(argv[1],"r");

    if(fin==NULL) {
        exit(2);
    }
    while(!feof(fin)){
        ch=fgetc(fin);
        if(ch=='\n') lines++;
    }

    fclose(fin);
    fin=fopen(argv[1],"r");

    while(!feof(fin)){
        ch=fgetc(fin);
        if(ch=='+' ||ch=='-'|| ch=='.'||ch=='X') rows++;
        if(ch=='\n') break;
    }

    printf("%d %d\n", lines, rows);
    fclose(fin);
    fin=fopen(argv[1],"r");

    while(!feof(fin)) {
        for(j=0; j<lines; j++){
            for(k=0; k<rows; k++){
                scanf(fin, "%c", &array[j][k]);
            }
        }

        //printf("%d %d", lines, rows);
        int i;
        for(i=0; i<lines; i++){
            for(j=0; j<rows; j++){
                printf("%c", array[i][j]);
                //printf("%d %d\n", i, j);

            }
        }
        fclose(fin);
        return 0;
    }
}

Answer 1

You have several problem in your code

1. See why while(foef(file)) is always wrong. If you are going to read the file character by characters, it's best to do it this way:

   int c;
   while((c = getchar()) != EOF)
   {
       // do somthing with c
   }
   

2. Reading the values like this fscanf(fin, "%c", &array[j][k]); it's ok, but it has one problem: you are forgetting to take the newline into account. You are only reading row number of characters, but the whole line (assuming there are no empty spaces and tabs) has row+1 characters, the newline didn't go away, so when you are finishing reading the last value of a row, the next scanf will not read the next value, it will read a newline. You can fix it by doing this:

   for(j=0; j<lines; j++){
       for(k=0; k<rows; k++){
           fscanf(fin, "%c", &array[j][k]);
   
       getchar(); // consume the newline
   }
   

In general you should read the values line by line using fgets and then you can use sscanf to parse the line.

So, to determine the number of lines:

int lines = 0;
int c, last = '\n';
while((c = fgetc(fin)) != EOF)
{
    last = c;
    if(c == '\n')
        lines++;
}

// in case the last line does not end with \n
// some file editors don't end the last line with \n
if(last != '\n')
    lines++;

To get the number of rows:

int rows = 0; 
while((c = fgetc(fin)) != EOF)
{
    // based on your example, the file does not
    // contains other characters than +,-,.,X and newlines
    if(ch == '\n')
        break;
    else
        rows++;
}

and now to read the values:

// assuming that the file has the correct format and that
// all lines have the same length
char line[rows+2];  // +2 because of the newline and the 0 terminating byte

for(int i = 0; i < lines && i < 1000; ++i)
{
    fgets(line, sizeof line, fin);
    char *tmp = line;
    for(int j = 0; j < rows && j < 1000; ++j)
        sscanf(tmp++, "%c", &array[i][j]);
}

Note that this code that the file has the proper format and that all lines have the same length. In order to make the reading more robust (that means that it can react to format errors) you'll need to check the return value of fgets and sscanf. I've omitted that for sake of simplicity, but you should add these checks.

And you don't need to open and close fin every time, you can use rewind(fin) to set the file at the beginning.

Answer 2

You can read the first line to get the number of rows.

// Read first line char by char
char ch = fgetc(fin);
while (ch != '\n' && !feof(fin)) {
    rows++;
    ch = fgetc(fin);
}

Read remaining lines to get number of lines

// Read remaining lines
while (!feof(fin)) {
    if (ch == '\n')
        lines++;
    ch = fgetc(fin);
}

Initialize array based on number of lines and rows and read through the file once again. Put non-newline characters to the appropriate location of the array by incrementing j after each character and i after each line.

// Initialize array, read again
rewind(fin);
char array[lines][rows];
printf("%d %d\n", lines, rows);

int i = 0; // Current line
int j = 0; // Current row
ch = fgetc(fin);
while (!feof(fin)) {
    if (ch != '\n') {
        array[i][j] = ch;
        j++;
    }
    else if (ch == '\n') {
        i++;
        j = 0;
    }
    ch = fgetc(fin);
}

Your read part terminates once it reaches end of file.

To print the array, it is a simple double-loop:

// Read array
for (i = 0; i < lines; i++) {
    printf("[");
    for (j = 0; j < rows; j++) {
    printf(" %c ", array[i][j]);
    }
    printf("]\n");
}