Using file handling read integers from file and display data in array - c

Question

# include <stdio.h>
main()
{
FILE *fp;
int a[10], n, i;
char file_name[20];
printf("enter the file name \n");
scanf("%s", file_name);
printf("enter number of integers \n");
scanf("%d", &n);
fp = fopen(file_name, "rb");
if (fp == NULL) {
printf("Error in opening file \n");
return;
}
fread(a, 1, n, fp);
for (i = 0; i < n; i++) {
printf("%d \n", a[i]);
}
}
Output:
enter the file name /home/n/t1.txt enter number of integers
3 1540736144 1540736144 1540736144..
In file t1.txt , i have entered the intergers {10,20,30,40.50}
and stored in path /home/n/t1.txt..
But in output it is displaying some junk addresses..
Kindly guide me how to display the integers stored in file..

Answer 1

Your file is a text file, which is human-readabla and can be edited in text editors. You treat it like a binary file, which stores data in the same way it is stored in the memory. Such files are compact and fast to read, but not easily editable or readable by humans.
The C standard provides different functions to deal with these file types. fwrite and fread are for binary files. fprintf, fscanf, fgets and so on are for text files.
There are several ways to parse your input and SO is full of examples. A cheap way to read data is fscanf. It ignores new-lines and just treats them as white space. It is not a good way to read input if you have more complex data or if you need good eror handling, but for your small example, it will do. Your input doesn't seem to be organised in lines.
The code below defines the function scan_int, which reads a number of integers from a file. The main function shows how to use this function.
#include <stdlib.h>
#include <stdio.h>
/*
* Read at most max integers from a file and store them in arr.
* Return the number of integers read or -1 on file access error.
* Numbers may or may not be separated with commas.
*/
int scan_int(const char *fn, int arr[], int max)
{
FILE *f = fopen(fn, "r");
int n = 0;
if (f == NULL) return -1;
while (n < max && fscanf(f, "%d,", &arr[n]) == 1) n++;
fclose(f);
return n;
}
int main(void)
{
int a[10];
int i, n;
n = scan_int("data.txt", a, 10);
for (i = 0; i < n; i++) {
if (i) printf(", ");
printf("%d", a[i]);
}
printf("\n");
return 0;
}