Curl 采集乱码与采集不到 PHP,该怎么处理

Curl 采集乱码与采集不到 PHP
PHP程序是用gbk2312编码的：

$url = "http://www.sina.com.cn";//gbk2312编码
//$url = "http://www.163.com";//gbk2312编码
//$url = "http://www.sohu.com";//gbk2312编码
 

  $ch = curl_init($url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER , true);//返回获取的输出的文本流
  $ret = curl_exec($ch);
  curl_setopt($ch, CURLOPT_TIMEOUT, 1);
  curl_close($ch);
  echo $ret;

?>

在采集sina.com.cn时，是正常的，但是采集163.com时是为空的，采集sohu.com时是丢码的.
这是怎么回事呢？如何解决？有哪位怎么呀？先谢谢了！！！没多少分了，不好意思。

------解决方案--------------------
别的不说,我就是来拿分的.楼主记得给全分

PHP code

$curl=curl_init('http://www.163.com');
curl_setopt($curl,CURLOPT_RETURNTRANSFER,1);
curl_setopt($curl,CURLOPT_USERAGENT,'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322)');
$html=curl_exec($curl);
var_dump($html);


$curl=curl_init('http://www.sohu.com');
curl_setopt($curl,CURLOPT_RETURNTRANSFER,1);
curl_setopt($curl,CURLOPT_USERAGENT,'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322)');
$html=curl_exec($curl);
//$html=strstr($html,' 0) {   
   switch ($method) {   
     case 8:   
       // Currently the only supported compression method:   
       $data = gzinflate($body);   
       break;   
     default:   
       // Unknown compression method   
       return false;   
   }   
  } else {   
   // I'm not sure if zero-byte body content is allowed.   
   // Allow it for now...  Do nothing...   
  }   
  
  // Verifiy decompressed size and CRC32:   
  // NOTE: This may fail with large data sizes depending on how   
  //      PHP's integer limitations affect strlen() since $isize   
  //      may be negative for large sizes.   
  if ($isize != strlen($data) || crc32($data) != $datacrc) {   
   // Bad format!  Length or CRC doesn't match!   
   return false;   
  }   
  return $data;   
}