PHP 防止外部提交表单|禁止跨站提交

$referer = isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : NULL;
$host = $_SERVER['HTTP_HOST'];
echo '提交过来的地址：'.$referer;
echo '
';
echo '本站域名：'.$host;
echo '
';
echo substr($referer,7,strlen($host));
if(substr($referer,7,strlen($host)) != $host){
 echo '非法操作';
}else{
 echo '正常操作';
}