Check if host is reachable?

Can php check if remote host is reachable?

[sunroof]

Does php have ability to check whether a website on the remote host is reachable or not?

Thanks.

[appi2]

<?php
$file = fopen ("http://www.example.com/", "r");
if (!$file) {
echo "<p>Unable to open remote file.\n";
exit;
}

many other ways.