unix programming C code problem

[May1911]

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <signal.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>

static void empty(int sig)
{
printf ("hello\n");
return;
}

void main()
{
int fd, a;
char buf[512];

if (fd = open("/tmp/nic", O_RDONLY) < 0)
{
perror ("open");
exit(1);
}

signal (SIGALRM, empty);
alarm (1);

a = read(fd, buf, 511);

while (a && a != -1) a = read(fd, buf, 511);

if (a == -1)
{
perror ("read");
exit(1);
}
else printf ("EOF\n");

exit(0);
}

Why isn't there any error Eintr ?