Reading from a text file and storing in a 2D array [duplicate]

Answer 1

You never change j, it always remains 0, so you're writing every position a[i][0]. atoi(line); will convert the first number in the line only. That's why your program is only storing the first column.

A possible approach to fix this would be something like:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int  i=0,totalNums,totalNum,j=0;
    size_t count;
    int numbers[100][100];
    char *line = malloc(100);

    FILE *file;  /* declare a FILE pointer  */
    file = fopen("g.txt", "r");  /* open a text file for reading */

    while(getline(&line, &count, file)!=-1) {
        for (; count > 0; count--, j++)
            sscanf(line, "%d", &numbers[i][j]);
        i++;
    }

    totalNums = i;
    totalNum = j;
    for (i=0 ; i<totalNums ; i++) {
      for (j=0 ; j<totalNum ; j++) {
        printf("\n%d",  numbers[i][j]);
      }
    }
    fclose(file);
    return 0;
}

That code will read the entire line, and then parse it number by number until no more numbers are there.

I didn't really understand if input is supposed to be integers or doubles, note that you declare a 2D array of doubles but then you call atoi(). The code I posted assumes it's integers, but then make sure to change your array to a 2D array of ints (or if they really are doubles, change the format string in sscanf).

Answer 2

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

int main(void)
{
  FILE * fp;
  char * line = NULL;
  size_t len = 0;
  ssize_t read;

  const char *s = " ";
  char *token = NULL;

  int i = 0;
  double arr[200];
  int j;

  fp = fopen("g.txt", "r");
  if (fp == NULL)
  {
    printf("Error opening");
    exit(EXIT_FAILURE);
  }

  while ((read=getline(&line, &len, fp)) != -1)
  {
     token = strtok(line, s);

     while(token != NULL)
     {
       arr[i] = atoi(token);
       printf("%f\n", arr[i]);
       token=strtok(NULL,s);
       i++;
     }
  }

  exit(EXIT_SUCCESS);
  return 0;
}

getline will read file line by line and strtok will split entries based on space and will store seperately entries in array. Also single dimensional array is enough to store values.