짧지만 php 코드 질문드립니다;;

재가 기초없이 공부해서 잘 모르겠네요;;
두줄의 php 문구인데요;; 해석좀 부탁드릴께요;;




(위에부분 코드)
$zipfile = array();
$fp = fopen("./data/zip1.db", "r");
while(!feof($fp)) {
$zipfile[] = fgets($fp, 4096);
}
fclose($fp);

$search_count = 0;

if ($addr1)
{
while ($zipcode = each($zipfile))
{
if(strstr(substr($zipcode[1],9,512), $addr1))
{
$list[$search_count][zip1] = substr($zipcode[1],0,3);
$list[$search_count][zip2] = substr($zipcode[1],4,3);
$addr = explode(" ", substr($zipcode[1],8));

if ($addr[sizeof($addr)-1])
{
$list[$search_count][addr] = str_replace($addr[sizeof($addr)-1], "", substr($zipcode[1],8));
$list[$search_count][bunji] = trim($addr[sizeof($addr)-1]);
}
else
$list[$search_count][addr] = substr($zipcode[1],8);

$list[$search_count][encode_addr] = urlencode($list[$search_count][addr]);
$search_count++;
}
}

if (!$search_count) alert("찾으시는 주소가 없습니다.");
}
-------------------------


substr($zipcode[1],9,512), $addr1)
ㄴ 여기서 $zipcode[1],9,512가 의미하는게 뭔지 모르겠네요;;

$addr[sizeof($addr)-1]
ㄴ sizeof는 count 랑 같다고하는데 왜 굳이 sizeof를 썻을까요??