FILE I/O operations. Clearing the elements of an structure - c

Question

I'm a begginer but I'm basically creating a program that opens a binary file containing 'parts' structure, reads the structure
into an array, sets the on_hand member of each structure to 0, and then writes the structure back to the file. Here's my code:
invclear.c
/* Modifies a file of part records by setting the quantity
on hand to a zero for all records */
#include <stdio.h>
#include <stdlib.h>
#define NAME_LEN 25
#define MAX_PARTS 100
struct part { //size= 36 bytes (2 holes in between number and name[] array
int number;
char name[NAME_LEN+1];
int on_hand;
}inventory[MAX_PARTS];
int num_parts;
int main()
{
FILE *fp;
int i;
if((fp=fopen("clear_sample.c", "rb+")) == NULL)
{
fprintf(stderr, "Can't open inventory file.\n");
exit(EXIT_FAILURE);
}
num_parts = fread(inventory, sizeof(struct part), MAX_PARTS, fp); //reads the contents
for(i=0; i<num_parts; i++)
inventory[i].on_hand=0; //clears them
rewind(fp); //sets file position at beggining
fwrite(inventory,sizeof(struct part), num_parts, fp);
fclose(fp);
return 0;
}
clear_sample.c
#include <stdio.h>
#include <stdlib.h>
#define NAME_LEN 25
#define MAX_PARTS 100
struct part {
int number;
char name[NAME_LEN+1];
int on_hand;
}inventory[MAX_PARTS]={0};
int main()
{
int i;
int num_parts;
for(i=1;i<=15;i++)
inventory[i].on_hand=i;
for(i=1;i<=15;i++)
printf("%d\n",inventory[i].on_hand);
return 0;
}
It runs without errors but unfortunately it's not clearing the on_hand variable to 0, in fact it's deleting almost the whole file. This is the modified clear_sample.c file that I get:
#include <stdio.h>
#include <st
Any ideas into why am I doing wrong would be greatly appreciated.

Answer 1

You have been misled by whatever tool you used to inspect the resulting file. It is not
#include <stdio.h>
#include <st
In fact it is
#include <stdio.h>
#include <std^#^#^#^#h>
#define NAME_LEN 25
#define ^#^#^#^#PARTS 100
struct part {
int^#^#^#^#ber;
char name[NAME_LEN+1];
^#^#^#^#int on_hand;
}inventory[MAX_^#^#^#^#S]={0};
int main()
{
int i^#^#^#^# int num_parts;
for(i=1;i<^#^#^#^#i++)
inventory[i].on_han^#^#^#^#
for(i=1;i<=15;i++)
^#^#^#^#ntf("%d\n",inventory[i].on_hand)^#^#^#^# return 0;
}
All those ^# are binary zero bytes, corresponding to zeroes you've put into on_hand.
As mentioned in comments, to test your program prepare a file which does obey the format you expect.