PHP未定义变量？

我购买GeoIP Web服务是为了从那里获取客户国的数据库IP，他们给我一个php代码，从那里获取响应API，告诉我IP来自哪个国家，下面是他们给我的代码：

    $query = "http://geoip.maxmind.com/f?l=" . $license_key . "&i=" . $ipaddress;
$url = parse_url($query);
$host = $url["host"];
$path = $url["path"] . "?" . $url["query"];
$timeout = 1;
$fp = fsockopen ($host, 80, $errno, $errstr, $timeout)
        or die('Can not open connection to server.');
if ($fp) {
  fputs ($fp, "GET $path HTTP/1.0\nHost: " . $host . "\n\n");
  while (!feof($fp)) {
    $buf .= fgets($fp, 128);
  }
  $lines = explode("\n", $buf);
  $data = $lines[count($lines)-1];
  fclose($fp);
} else {
  # enter error handing code here
}
echo $data;

我得到$data值，它告诉我$ipaddress从哪里来。。。。。。但我得到一个错误：未定义变量$buf？

Add

$buf = '';

在代码上方

将代码更改为：

$query = "http://geoip.maxmind.com/f?l=" . $license_key . "&i=" . $ipaddress;
$url = parse_url($query);
$host = $url["host"];
$path = $url["path"] . "?" . $url["query"];
$timeout = 1;
$fp = fsockopen ($host, 80, $errno, $errstr, $timeout)
        or die('Can not open connection to server.');

if ($fp) {
  fputs ($fp, "GET $path HTTP/1.0\nHost: " . $host . "\n\n");
  $buf = ''; //This is the line of code that initializes $buf and will keep the undefined error from happening 
 while (!feof($fp)) {
    $buf .= fgets($fp, 128);
  }
  $lines = explode("\n", $buf);
  $data = $lines[count($lines)-1];
  fclose($fp);
} else {
  # enter error handing code here
}
echo $data;

---

关于这条信息，到底有什么不清楚的地方PIs$buf已初始化？我不认为可以连接一个未定义的变量来初始化它。