Question

char buf[BUF_LEN]_attribute_((aligned(4)));
ssize_t len, i = 0;
/* read BUF_LEN bytes' worth of events */
len = read (fd, buf, BUF_LEN);
/* loop over every read event until none remain */
while (i < len) {
struct inotify_event *event =
(struct inotify_event *) &buf[i];
Monitoring File Events | 239
printf ("wd=%d mask=%d cookie=%d len=%d dir=%s\n",
event->wd, event->mask,
event->cookie, event->len,
(event->mask & IN_ISDIR) ? "yes" : "no");
/* if there is a name, print it */
if (event->len)
printf ("name=%s\n", event->name);
/* update the index to the start of the next event */
i += sizeof (struct inotify_event) + event->len;
}

Answer 1

char buf[BUF_LEN]_attribute_((aligned(4)));

It specifies a minimum alignment for the variable buf, measured in bytes.
It causes the compiler to allocate the variable buf on a 4-byte boundary.

This should be a good read.