summaryrefslogtreecommitdiff
path: root/reference/C/CONTRIB/OR_USING_C/03.2.c
blob: 69d890499b76d36edf8cc5131d097fe486c81b76 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
/*
 * If you're on System V, change <sys/file.h> to <sys/fcntl.h>.
 */
#include <sys/file.h>

struct record {
    int uid;
    char login[9];
};

char *logins[] = { "user1", "user2", "user3",
                   "user4", "user5" };

main()
{
    int i, fd;
    struct record rec;

    /*
     * Open the data file for writing.
     */
    if ((fd = open("datafile", O_WRONLY | O_CREAT, 0644)) < 0) {
        perror("datafile");
        exit(1);
    }

    /*
     * For each user, going backwards...
     */
    for (i = 4; i >= 0; i--) {
        /*
         * Create the record.
         */
        rec.uid = i;
        strcpy(rec.login, logins[i]);

        /*
         * Output the record.  Notice we pass the
         * address of the structure.
         */
        putrec(fd, i, &rec);
    }

    close(fd);
    exit(0);
}

/*
 * putrec--write the record in the i'th position.
 */
putrec(fd, i, r)
int i, fd;
struct record *r;
{
    /*
     * Seek to the i'th position from the beginning
     * of the file.
     */
    lseek(fd, (long) i * sizeof(struct record), L_SET);

    /*
     * Write the record.  We want to write one
     * object the size of a record structure.
     */
    write(fd, r, sizeof(struct record));
}