php用Curl的post方法只获取header头信息中的Location

<?php
$posturl = "http://www.baidu.com/";
$postdata = "a=1&b=2";
$ch = curl_init();
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_URL,$posturl);
curl_setopt($ch, CURLOPT_REFERER,"");

//REFERER  
curl_setopt($ch, CURLOPT_POSTFIELDS, $postdata);
curl_setopt($ch, CURLOPT_HEADER, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$content = curl_exec($ch);
curl_close($ch);

// 解析HTTP数据流   
list($header, $body) = explode("\r\n\r\n", $content);
preg_match("/Location:([^\r\n]*)/i", $header, $matches);
$Location = $matches[1];
if($Location != ""){
    echo $Location;
}else{
    echo "未获取到";
}
?>