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XCVIII. SimpleXML functions

介绍

警告

本扩展模块是实验性的。该模块的行为，包括其函数的名称以及其它任何关于此模块的文档可能会在没有通知的情况下随 PHP 以后的发布而改变。我们提醒您在使用本扩展模块的同时自担风险。

The SimpleXML extension provides a very simple and easily usable toolset to convert XML to an object that can be processed with normal property selectors and array iterators.

安装

This extension is only available if PHP was configured with --enable-simplexml. The PHP configuration script does this by default.

范例

Many examples in this reference require an XML string. Instead of repeating this string in every example, we put it into a file which we include in each example. This included file is shown in the following example section. Alternatively, you could create an XML document and read it with simplexml_load_file().

例子 1. Include file example.php with XML string

<?php
$xmlstr = <<<XML
<?xml version='1.0' standalone='yes'?>
<movies>
<movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Ms. Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#211;r</actor>
   </character>
  </characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
</movie>
</movies>
XML;?>

The simplicity of SimpleXML appears most clearly when one extracts a string or number from a basic XML document.

例子 2. Getting <plot>

<?php
include 'example.php';

$xml = simplexml_load_string($xmlstr);

echo $xml->movie[0]->plot; // "So this language. It's like..."
?>

例子 3. Accessing non-unique elements in SimpleXML

When multiple instances of an element exist as children of a single parent element, normal iteration techniques apply.

<?php
include 'example.php';

$xml = simplexml_load_string($xmlstr);

/* For each <movie> node, we echo a separate <plot>. */
foreach ($xml->movie as $movie) {
   echo $movie->plot, '<br />';
}

?>

例子 4. Using attributes

So far, we have only covered the work of reading element names and their values. SimpleXML can also access element attributes. Access attributes of an element just as you would elements of an array.

<?php
include 'example.php';

$xml = simplexml_load_string($xmlstr);

/* Access the <rating> nodes of the first movie.
* Output the rating scale, too. */
foreach ($xml->movie[0]->rating as $rating) {
    switch((string) $rating['type']) { // Get attributes as element indices
    case 'thumbs':
        echo $rating, ' thumbs up';
        break;
    case 'stars':
        echo $rating, ' stars';
        break;
    }
}
?>

例子 5. Comparing Elements and Attributes with Text

To compare an element or attribute with a string or pass it into a function that requires a string, you must cast it to a string using (string). Otherwise, PHP treats the element as an object.

<?php     
include 'example.php';

$xml = simplexml_load_string($xmlstr);

if ((string) $xml->movie->title == 'PHP: Behind the Parser') {
    print 'My favorite movie.';
}

htmlentities((string) $xml->movie->title);
?>

例子 6. Using Xpath

SimpleXML includes builtin Xpath support. To find all <character> elements:

<?php
include 'example.php';
$xml = simplexml_load_string($xmlstr);

foreach ($xml->xpath('//character') as $character) {
    echo $character->name, 'played by ', $character->actor, '<br />';
}
?>

'//' serves as a wildcard. To specify absolute paths, omit one of the slashes.

例子 7. Setting values

Data in SimpleXML doesn't have to be constant. The object allows for manipulation of all of its elements.

<?php
include 'example.php';
$xml = simplexml_load_string($xmlstr);

$xml->movie[0]->actor[0]->age = '21';

echo $xml->asXML();
?>

The above code will output a new XML document, just like the original, except that the new XML will define Ms. Coder's age as 21.

例子 8. DOM Interoperability

PHP has a mechanism to convert XML nodes between SimpleXML and DOM formats. This example shows how one might change a DOM element to SimpleXML.

<?php
$dom = new domDocument;
$dom->loadXML('<books><book><title>blah</title></book></books>');
if (!$dom) {
     echo 'Error while parsing the document';
     exit;
}

$s = simplexml_import_dom($dom);

echo $s->book[0]->title;
?>

目录
simplexml_element->asXML --  Return a well-formed XML string based on SimpleXML element.
simplexml_element->attributes --  Identifies an element's attributes.
simplexml_element->children --  Finds children of given node.
simplexml_element->xpath --  Runs Xpath query on XML data.
simplexml_import_dom --  Get a simplexml_element object from a DOM node.
simplexml_load_file --  Interprets an XML file into an object.
simplexml_load_string --  Interprets a string of XML into an object.


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