File input

Reading an array of integers from a file

This example uses the feof() function to read from the file until it is empty. Obviously, I am assuming the file consists of a list of 20 or fewer integers and that the last integer is on the last line of the file (i.e. no extraneous lines at the end of the file).

#include <stdio.h>

int main(void)
{
  FILE *ptr;
  int index, array[20], i = 0, flag, temp;

  ptr = fopen("test.dat", "r");
  
  while (!feof(ptr))
  {
    flag = fscanf(ptr, "%d", &temp);
    if (flag == 1)
    {
       array[i] = temp;
       i++;
    }
  }
  fclose(ptr);
  i--;
  printf("\n");
  for (index = 0; index <= i; index++)
    printf("%d ", array[index]);
  printf("\n\n"); 

  return (0);
}

This example simply compares the return value of the fscanf() to EOF to determine whether the end of the file has been reached. As with the first example, no error checking has been done.

#include <stdio.h>

int main(void)
{
  FILE *ptr;
  int index, array[20], i = 0, flag, temp;

  ptr = fopen("test.dat", "r");
  
  do
  {
    flag = fscanf(ptr, "%d", &temp);
    if (flag == 1)
    {
       array[i] = temp;
       i++;
    }
  }
  while (flag != EOF);
  fclose(ptr);
  i--;
  printf("\n");
  for (index = 0; index <= i; index++)
    printf("%d ", array[index]);
  printf("\n\n"); 

  return (0);
}

This is the file I used to test the 2 samples. The 1 is the first character in the file and the 89 is on the last line (i.e. no carriage return or white space followed the 89).