PHP: Basic SimpleXML usage

Basic SimpleXML usage

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().

示例 #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>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <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.

示例 #2 Getting <plot>

<?php
include 'example.php';

$movies = new SimpleXMLElement($xmlstr);

echo $movies->movie[0]->plot;
?>

以上示例会输出：


   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.

Accessing elements within an XML document that contain characters not permitted under PHP's naming convention (e.g. the hyphen) can be accomplished by encapsulating the element name within braces and the apostrophe.

示例 #3 Getting <line>

<?php
include 'example.php';

$movies = new SimpleXMLElement($xmlstr);

echo $movies->movie->{'great-lines'}->line;
?>

以上示例会输出：

PHP solves all my web problems

示例 #4 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';

$movies = new SimpleXMLElement($xmlstr);

/* For each <character> node, we echo a separate <name>. */
foreach ($movies->movie->characters->character as $character) {
   echo $character->name, ' played by ', $character->actor, PHP_EOL;
}

?>

以上示例会输出：

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

注意:
Properties ($movies->movie in previous example) are not arrays. They are iterable and accessible objects.

示例 #5 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';

$movies = new SimpleXMLElement($xmlstr);

/* Access the <rating> nodes of the first movie.
 * Output the rating scale, too. */
foreach ($movies->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;
    }
}
?>

以上示例会输出：

7 thumbs up5 stars

示例 #6 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';

$movies = new SimpleXMLElement($xmlstr);

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

echo htmlentities((string) $movies->movie->title);
?>

以上示例会输出：

My favorite movie.PHP: Behind the Parser

示例 #7 Comparing Two Elements

Two SimpleXMLElements are considered different even if they point to the same element.

<?php
include 'example.php';

$movies1 = new SimpleXMLElement($xmlstr);
$movies2 = new SimpleXMLElement($xmlstr);
var_dump($movies1 == $movies2);
?>

以上示例会输出：

bool(false)

示例 #8 Using XPath

SimpleXML includes built-in XPath support. To find all <character> elements:

<?php
include 'example.php';

$movies = new SimpleXMLElement($xmlstr);

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

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

以上示例会输出：

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

示例 #9 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';
$movies = new SimpleXMLElement($xmlstr);

$movies->movie[0]->characters->character[0]->name = 'Miss Coder';

echo $movies->asXML();
?>

以上示例会输出：

<?xml version="1.0" standalone="yes"?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Miss Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#xD3;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>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 </movie>
</movies>

示例 #10 Adding elements and attributes

SimpleXML has had the ability to easily add children and attributes.

<?php
include 'example.php';
$movies = new SimpleXMLElement($xmlstr);

$character = $movies->movie[0]->characters->addChild('character');
$character->addChild('name', 'Mr. Parser');
$character->addChild('actor', 'John Doe');

$rating = $movies->movie[0]->addChild('rating', 'PG');
$rating->addAttribute('type', 'mpaa');

echo $movies->asXML();
?>

以上示例会输出：

<?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&#xD3;r</actor>
   </character>
  <character><name>Mr. Parser</name><actor>John Doe</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>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 <rating type="mpaa">PG</rating></movie>
</movies>

示例 #11 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;
}

$books = simplexml_import_dom($dom);

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

以上示例会输出：

blah

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用户贡献的备注 9 notes

down

rowan dot collins at gmail dot com ¶

9 years ago

There is a common "trick" often proposed to convert a SimpleXML object to an array, by running it through json_encode() and then json_decode(). I'd like to explain why this is a bad idea.

Most simply, because the whole point of SimpleXML is to be easier to use and more powerful than a plain array. For instance, you can write <?php $foo->bar->baz['bing'] ?> and it means the same thing as <?php $foo->bar[0]->baz[0]['bing'] ?>, regardless of how many bar or baz elements there are in the XML; and if you write <?php (string)$foo->bar[0]->baz[0] ?> you get all the string content of that node - including CDATA sections - regardless of whether it also has child elements or attributes. You also have access to namespace information, the ability to make simple edits to the XML, and even the ability to "import" into a DOM object, for much more powerful manipulation. All of this is lost by turning the object into an array rather than reading understanding the examples on this page.

Additionally, because it is not designed for this purpose, the conversion to JSON and back will actually lose information in some situations. For instance, any elements or attributes in a namespace will simply be discarded, and any text content will be discarded if an element also has children or attributes. Sometimes, this won't matter, but if you get in the habit of converting everything to arrays, it's going to sting you eventually.

Of course, you could write a smarter conversion, which didn't have these limitations, but at that point, you are getting no value out of SimpleXML at all, and should just use the lower level XML Parser functions, or the XMLReader class, to create your structure. You still won't have the extra convenience functionality of SimpleXML, but that's your loss.

down

jishcem at gmail dot com ¶

11 years ago

For me it was easier to use arrays than objects, 

So, I used this code, 

$xml = simplexml_load_file('xml_file.xml');
    
$json_string = json_encode($xml);
    
$result_array = json_decode($json_string, TRUE);

Hope it would help someone

down

Anonymous ¶

7 years ago

If your xml string contains booleans encoded with "0" and "1", you will run into problems when you cast the element directly to bool:

$xmlstr = <<<XML
<?xml version='1.0' standalone='yes'?>
<values>
    <truevalue>1</truevalue>
    <falsevalue>0</falsevalue>
</values>
XML;
$values = new SimpleXMLElement($xmlstr);
$truevalue = (bool)$values->truevalue; // true
$falsevalue = (bool)$values->falsevalue; // also true!!!

Instead you need to cast to string or int first:

$truevalue = (bool)(int)$values->truevalue; // true
$falsevalue = (bool)(int)$values->falsevalue; // false

down

Josef ¶

3 years ago

How to find out if a Node exists:

<?xml version='1.0' standalone='yes'?>
<book>
  <author>Josef</author>
  <isbn></isbn>
</book>

empty($xml->isbn) will be true
isset($xml->isbn) will be true

empty($xml->title) will be true
isset($xml->title) will be false

down

ie dot raymond at gmail dot com ¶

14 years ago

If you need to output valid xml in your response, don't forget to set your header content type to xml in addition to echoing out the result of asXML():



<?php



$xml=simplexml_load_file('...');

...

...xml stuff

...



//output xml in your response:

header('Content-Type: text/xml');

echo $xml->asXML();

?>

down

gkokmdam at zonnet dot nl ¶

13 years ago

A quick tip on xpath queries and default namespaces. It looks like the XML-system behind SimpleXML has the same workings as I believe the XML-system .NET uses: when one needs to address something in the default namespace, one will have to declare the namespace using registerXPathNamespace and then use its prefix to address the otherwise in the default namespace living element.

<?php
$string = <<<XML
<?xml version='1.0'?> 
<document xmlns="http://www.w3.org/2005/Atom">
 <title>Forty What?</title>
 <from>Joe</from>
 <to>Jane</to>
 <body>
  I know that's the answer -- but what's the question?
 </body>
</document>
XML;

$xml = simplexml_load_string($string);
$xml->registerXPathNamespace("def", "http://www.w3.org/2005/Atom");

$nodes = $xml->xpath("//def:document/def:title");

?>

down

kdos ¶

13 years ago

Using stuff like: is_object($xml->module->admin) to check if there actually is a node called "admin", doesn't seem to work as expected, since simplexml always returns an object- in that case an empty one  - even if a particular node does not exist. 
For me good old empty() function seems to work just fine in such cases.

Cheers

down

Max K. ¶

14 years ago

From the README file:

SimpleXML is meant to be an easy way to access XML data.

SimpleXML objects follow four basic rules:

1) properties denote element iterators
2) numeric indices denote elements
3) non numeric indices denote attributes
4) string conversion allows to access TEXT data

When iterating properties then the extension always iterates over
all nodes with that element name. Thus method children() must be 
called to iterate over subnodes. But also doing the following:
foreach ($obj->node_name as $elem) {
  // do something with $elem
}
always results in iteration of 'node_name' elements. So no further 
check is needed to distinguish the number of nodes of that type.

When an elements TEXT data is being accessed through a property
then the result does not include the TEXT data of subelements.

Known issues
============

Due to engine problems it is currently not possible to access
a subelement by index 0: $object->property[0].

down

-1

php at keith tyler dot com ¶

14 years ago

[Editor's Note: The SimpleXMLIterator class, however, does implement these methods.]



While SimpleXMLElement claims to be iterable, it does not seem to implement the standard Iterator interface functions like ::next and ::reset properly. Therefore while foreach() works, functions like next(), current(), or each() don't seem to work as you would expect -- the pointer never seems to move or keeps getting reset.