PHP SimpleXML 完整指南：載入、解析與巡覽 XML 文件

核心函數

• simplexml_load_file($file)：從檔案/URL 載入 → SimpleXMLElement 物件。
• simplexml_load_string($xml)：從字串載入。
• new SimpleXMLElement($file, 0, true)：從檔案建立（第 3 參數 true 表 dataIsURL）。

範例 XML：books.xml

<?xml version="1.0" standalone="yes"?>
<library>
  <book>
    <title>Pride and Prejudice</title>
    <author gender="female">Jane Austen</author>
    <description>Jane Austen's most popular work.</description>
  </book>
  <book>
    <title>The Conformist</title>
    <author gender="male">Alberto Moravia</author>
    <description>Alberto Moravia's classic psyhcological novel.</description>
  </book>
  <book>
    <title>The Sun Also Rises</title>
    <author gender="male">Ernest Hemingway</author>
    <description>The masterpiece that launched Hemingway's career.</description>
  </book>
</library>

載入與結構檢視

$xml = simplexml_load_file('books.xml');
echo '<pre>';
var_dump($xml);

輸出結構：

object(SimpleXMLElement)#1 (1) {
  ["book"]=>
  array(3) {
    [0]=> object(SimpleXMLElement)#2 (3) { ["title"]=> "Pride and Prejudice", ["author"]=> "Jane Austen", ["description"]=> "..." }
    [1]=> object(SimpleXMLElement)#3 (3) { ["title"]=> "The Conformist", ["author"]=> "Alberto Moravia", ["description"]=> "..." }
    [2]=> object(SimpleXMLElement)#4 (3) { ["title"]=> "The Sun Also Rises", ["author"]=> "Ernest Hemingway", ["description"]=> "..." }
  }
}

巡覽與存取

// 迴圈所有 book
foreach ($xml->book as $book) {
    echo (string)$book->title . "\n";
    echo (string)$book->author . "\n";
    // 存取屬性
    echo (string)$book->author['gender'] . "\n";
}

// XPath 查詢
$femaleBooks = $xml->xpath('//book/author[@gender="female"]/..');
foreach ($femaleBooks as $b) {
    echo (string)$b->title . " (female author)\n";
}

// 修改並儲存
$xml->book[0]->title = 'New Title';
$xml->asXML('books_modified.xml');

常見陷阱

• SimpleXMLElement 物件需轉型 才能正常輸出/比較：(string)$node、(int)$node。
• 命名空間需註冊前綴：$xml->registerXPathNamespace('ns', 'https://...')。
• 大型 XML（>100MB）會耗盡記憶體，改用 XMLReader 流式解析。
• CDATA 區塊自動解析為文字節點，無需特殊處理。

結語

SimpleXML 以極簡 API 處理 95% XML 需求，配合 XPath 強大查詢，是 PHP 處理設定檔、API 回應、RSS/Atom 的首選工具。