将元素和节点添加到现有xml中

<?xml version="1.0"?>
<users><user><firstname>ben</firstname><surname>kim</surname
<email>benkim@test.com</email></user>
<user><firstname>ken</firstname><surname>kim</surname><email>kenkim@test.com</email>   
</user></users>

<?php
    header('Content-Type: text/xml');
?>
<?php
    $firstname = $_GET["firstname"];
    $surname = $_GET["surname"];
    $email = $_GET["email"];
    $person = array("firstname"=>$firstname,"surname"=>$surname,"email"=>$email);
    //ECHO (fromXML());
    $xmlDoc = new DOMDocument();
    $xmlDoc->load("test.xml");
    $xmlDoc=$xmlDoc->documentElement;
    toXml($person);
    function toXml($person)
    {
        $users = $xmlDoc->getElementsByTagName('users');
        $user = $xmlDoc->createElement('user');
        $user = $users->appendChild($user);
        $firstname = $xmlDoc->createElement('firstname'); 
        $firstname = $user->appendChild($firstname);   
        $valFirstname = $xmlDoc->createTextNode($person["firstname"]);
        $valFirstname = $firstname->appendChild($valFirstname);
        $surname = $xmlDoc->createElement('surname'); 
        $surname = $user->appendChild($surname);   
        $valSurname = $xmlDoc->createTextNode($person["surname"]);
        $valSurname = $surname->appendChild($valSurname);
        $email = $xmlDoc->createElement('email'); 
        $email = $user->appendChild($email);   
        $valEmail = $xmlDoc->createTextNode($person["email"]);
        $valEmail = $email->appendChild($valEmail);
        $strXml = $xmlDoc->saveXML();
        $handle = fopen("test.xml", "a");
        fwrite($handle, $strXml);
        fclose($handle);
    }

您有多个问题。

首先，$xmlDoc在您的函数范围内不可用。为此，您需要：

• 将$xmlDoc作为toXml()函数的参数传递（推荐使用）
• 使用global关键字告诉函数它需要从全局上下文中获取$xmlDoc（这是不鼓励的）

然后，您无法正确获取根节点。在您的情况下，您只需要使用$xmlDoc->firstChild获取它。

然后，您需要创建不同的节点，然后将它们插入到根节点中。这意味着您需要在将元素附加到DOM之前创建这些元素。

最后，您将以追加模式打开test.xml文件（a）。这意味着，当您保存文档时，实际上会将xml的内容附加到现有内容中，因此，您的文档将无效，因为每次执行脚本时，它都会有一个新的<?xml ... ?>标记。

这是您的脚本的更正版本。如果您有任何问题，请随时提问！：）

<?php
$person = array(
    "firstname" => $_GET["firstname"],
    "surname"   => $_GET["surname"],
    "email"     => $_GET["email"],
);
$xmlDoc = new DOMDocument();
$xmlDoc->preserveWhiteSpace = false;
$xmlDoc->formatOutput = true;
$xmlDoc->load("test.xml");
toXml($person, $xmlDoc);
header('Content-Type', 'application/xml');
exit(file_get_contents('test.xml'));
function toXml(array $person, DOMDocument $xmlDoc)
{
    $users = $xmlDoc->firstChild;
    $user = $xmlDoc->createElement('user');
    $firstname = $xmlDoc->createElement('firstname');
    $textNode = $xmlDoc->createTextNode($person["firstname"]);
    $firstname->appendChild($textNode);
    $user->appendChild($firstname);
    $surname = $xmlDoc->createElement('surname');
    $textNode = $xmlDoc->createTextNode($person["surname"]);
    $surname->appendChild($textNode);
    $user->appendChild($surname);
    $email = $xmlDoc->createElement('email');
    $textNode = $xmlDoc->createTextNode($person["email"]);
    $email->appendChild($textNode);
    $user->appendChild($email);
    $users->appendChild($user);
    $strXml = $xmlDoc->saveXML();
    $handle = fopen("test.xml", "w");
    fwrite($handle, $strXml);
    fclose($handle);
}

尝试使用SimpleXML而不是

$xml = new SimpleXMLElement('your xml here');
$user = $xml->addChild('user');
$user->addChild('firstname', $person["firstname"]);