我有以下这段XML：
<?xml version="1.0" encoding="UTF-8"?>
<searchRetrieveResponse xmlns="http://www.loc.gov/zing/srw/">
<version>1.1</version>
<numberOfRecords>1</numberOfRecords>
<records>
<record>
<recordSchema>MARC21-xml</recordSchema>
<recordPacking>xml</recordPacking>
<recordData>
<record xmlns="http://www.loc.gov/MARC21/slim" type="Authority">
<leader>00000nz a2200000nc 4500</leader>
<controlfield tag="001">040432386</controlfield>
<controlfield tag="003">DE-101</controlfield>
<controlfield tag="005">20180124053847.0</controlfield>
<controlfield tag="008">880701n||azznnbabn | ana |c</controlfield>
<datafield tag="024" ind1="7" ind2=" ">
<subfield code="a">http://d-nb.info/gnd/4043238-5</subfield>
<subfield code="2">uri</subfield>
</datafield>
<datafield tag="035" ind1=" " ind2=" ">
<subfield code="a">(DE-101)040432386</subfield>
</datafield>
<datafield tag="035" ind1=" " ind2=" ">
<subfield code="a">(DE-588)4043238-5</subfield>
</datafield>
<datafield tag="035" ind1=" " ind2=" ">
<subfield code="z">(DE-588c)4043238-5</subfield>
<subfield code="9">v:zg</subfield>
</datafield>
<datafield tag="040" ind1=" " ind2=" ">
<subfield code="a">DE-101</subfield>
<subfield code="9">r:DE-101</subfield>
<subfield code="b">ger</subfield>
<subfield code="d">9999</subfield>
</datafield>
<datafield tag="042" ind1=" " ind2=" ">
<subfield code="a">gnd1</subfield>
</datafield>
<datafield tag="065" ind1=" " ind2=" ">
<subfield code="a">13.3</subfield>
<subfield code="2">sswd</subfield>
</datafield>
<datafield tag="075" ind1=" " ind2=" ">
<subfield code="b">s</subfield>
<subfield code="2">gndgen</subfield>
</datafield>
<datafield tag="075" ind1=" " ind2=" ">
<subfield code="b">saz</subfield>
<subfield code="2">gndspec</subfield>
</datafield>
<datafield tag="079" ind1=" " ind2=" ">
<subfield code="a">g</subfield>
<subfield code="q">s</subfield>
<subfield code="u">w</subfield>
<subfield code="u">o</subfield>
<subfield code="u">z</subfield>
</datafield>
<datafield tag="083" ind1="0" ind2="4">
<subfield code="a">751.45</subfield>
<subfield code="9">d:3</subfield>
<subfield code="9">t:2007-01-01</subfield>
<subfield code="2">22/ger</subfield>
</datafield>
<datafield tag="150" ind1=" " ind2=" ">
<subfield code="a">Ölmalerei</subfield>
</datafield>
<datafield tag="450" ind1=" " ind2=" ">
<subfield code="a">Ölgemälde</subfield>
</datafield>
<datafield tag="550" ind1=" " ind2=" ">
<subfield code="0">(DE-101)040372200</subfield>
<subfield code="0">(DE-588)4037220-0</subfield>
<subfield code="0">http://d-nb.info/gnd/4037220-0</subfield>
<subfield code="a">Malerei</subfield>
<subfield code="4">obal</subfield>
<subfield code="4">http://d-nb.info/standards/elementset/gnd#broaderTermGeneral</subfield>
<subfield code="w">r</subfield>
<subfield code="i">Oberbegriff allgemein</subfield>
</datafield>
<datafield tag="670" ind1=" " ind2=" ">
<subfield code="a">M</subfield>
</datafield>
<datafield tag="677" ind1=" " ind2=" ">
<subfield code="a">Wird i.d.R. nur verwendet, wenn die Maltechnik behandelt ist.</subfield>
</datafield>
<datafield tag="750" ind1=" " ind2="7">
<subfield code="a">Peinture à l'huile</subfield>
<subfield code="0">(FrPBN)FRBNF119329441</subfield>
<subfield code="0">http://data.bnf.fr/11932944</subfield>
<subfield code="2">ram</subfield>
<subfield code="9">v:MACS-Mapping. Bitte keine Änderungen vornehmen.</subfield>
</datafield>
<datafield tag="913" ind1=" " ind2=" ">
<subfield code="S">swd</subfield>
<subfield code="i">s</subfield>
<subfield code="a">Ölmalerei</subfield>
<subfield code="0">(DE-588c)4043238-5</subfield>
</datafield>
</record>
</recordData>
<recordPosition>1</recordPosition>
</record>
</records>
<nextRecordPosition>2</nextRecordPosition>
<echoedSearchRetrieveRequest>
<version>1.1</version>
<query>WOE=4043238-5 and COD=s</query>
<xQuery xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true" />
<recordSchema>MARC21-xml</recordSchema>
</echoedSearchRetrieveRequest>
<extraResponseData>
<accountOf xmlns="">Staatsbibliothek zu Berlin - Preußischer Kulturbesitz, bpk-Bildagentur</accountOf>
</extraResponseData>
</searchRetrieveResponse>
当我在下面运行我的PHP代码时，我只会得到一个空白页。例如，缺少datafield 150和相应的tag来访问subfield的哪个代码？我想念什么？
php代码：
header('Content-type: text/html; charset=utf-8');
error_reporting(E_ALL);
$id = $_POST["id"];
// URL to fetch
$url = "https://services.dnb.de/sru/authorities?version=1.1&operation=searchRetrieve&query=WOE%3D$id%20and%20COD%3Ds&recordSchema=MARC21-xml";
// Setting the HTTP Request Headers
$User_Agent = 'Mozilla/5.0 (Windows NT 6.1; rv:60.0) Gecko/20100101 Firefox/60.0';
$request_headers = array('Contect-Type:text/xml', 'Accept:text/xml');
$ch = curl_init($url);
// Set the url
curl_setopt( $ch, CURLOPT_URL, $url );
curl_setopt($ch, CURLOPT_USERAGENT, $User_Agent);
curl_setopt($ch, CURLOPT_HTTPHEADER, $request_headers);
curl_setopt($ch, CURLOPT_ENCODING, "");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
// Execute
$result = curl_exec($ch); // Performs the Request, with specified curl_setopt() options (if any).
// Closing
curl_close($ch);
$xml = SimpleXMLElement($result) or die("Error: Cannot create object");
echo($xml);
我环顾四周，发现可能与将其传递给字符串有关，但随后在屏幕上却什么也没得到。甚至没有SimpleXMLElement对象。
感谢您的帮助
答案 0 :(得分：1)
SimpleXMLElement是一个类名，而不是一个函数。尝试使用new实例化它：
$xml = new SimpleXMLElement($result);
或者改用simplexml_load_string。
$xml = simplexml_load_string($result);
此外，使用所有curl代码会使事情变得过于复杂。这应该同样有效：
// ALWAYS sanitize user-submitted data
// in this example everything except numbers and hyphens are removed
$id = preg_replace("/[^0-9-]/", "", $_POST["id"]);
$url = "https://services.dnb.de/sru/authorities?version=1.1&operation=searchRetrieve&query=WOE%3D$id%20and%20COD%3Ds&recordSchema=MARC21-xml";
$xml = new SimpleXMLElement($url, 0, true);
答案 1 :(得分：0)
评论和其他答案涵盖了您未获得任何输出的原因。这是因为缺少new关键字。这将向您展示如何获取结果对象并解析它以获得所需的子字段。这只是转储子字段对象，但是您可以从此处使用它进行任何操作。
$xmlObj = new SimpleXMLElement($xml);
foreach($xmlObj->records->record->recordData->record->datafield as $dfield)
{
if((string)$dfield["tag"] == "150")
{
$subfield = $dfield->subfield;
var_dump($subfield);
}
}