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/*
* 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));
}
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