Thread: structures

I can't understand this code

Code:

#include <stdio.h>

/* random record description - could be anything */
struct rec
{
    int x,y,z;
};

/* writes and then reads 10 arbitrary records
   from the file "junk". */
int main()
{
    int i,j;
    FILE *f;
    struct rec r;

    /* create the file of 10 records */
    f=fopen("junk","w");
    if (!f)
        return 1;
    for (i=1;i<=10; i++)
    {
        r.x=i;
        fwrite(&r,sizeof(struct rec),1,f);
    }
    fclose(f);

    /* read the 10 records */
    f=fopen("junk","r");
    if (!f)
        return 1;
    for (i=1;i<=10; i++)
    {
        fread(&r,sizeof(struct rec),1,f);
        printf("%d\n",r.x);
    }
    fclose(f);
     
    return 0;
}

The bit I'm confused about is the bit where the program writes a number to the structure then to the file

Code:

for (i=1;i<=10; i++)
    {
        r.x=i;
        fwrite(&r,sizeof(struct rec),1,f);
    }

doesn't this mean r.x = the value of i, but once it loops around would r.x equal the new value of i and wipe the old value out of its memory?

ahhh I think i get it, when you save r.x to a file it dosn't overwirte any previous r.x's but in the program it will.

Please tell me if you think I am worng!