XML operation of PHP extension (1)-SimpleXML

1. Introduction and installation

SimpleXML extension provides a very simple and easy-to-use toolset that can convert XML into an XML file with general attribute selectors and An object for array iterators.

This extension requires the libxml PHP extension. This means that --enable-libxml needs to be used, although this will be done implicitly since libxml is enabled by default.

Requires PHP5 and above.

This extension is enabled by default and can be disabled through the following options when compiling: --disable-simplexml

2. Usage examples

Basic usage

Example #1 Include file example.php with XML string

<?php
$xmlstr = <<<XML
<?xml version=&#39;1.0&#39; standalone=&#39;yes&#39;?>
<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&#39;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.

Example #2 Getting

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
echo $movies->movie[0]->plot;?>

The above routine will output:

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.

Example #3 Getting

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
echo $movies->movie->{&#39;great-lines&#39;}->line;?>

The above routine will output:

PHP solves all my web problems

Example #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.

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
/* For each <character> node, we echo a separate <name>. */foreach ($movies->movie->characters->character as $character) {
echo $character->name, &#39; played by &#39;, $character->actor, PHP_EOL;}
?>

The above routine will output:

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

Note:

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

Example #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.

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
/* Access the <rating> nodes of the first movie.* Output the rating scale, too. */
foreach ($movies->movie[0]->rating as $rating) {
switch((string) $rating[&#39;type&#39;]) { // Get attributes as element indicescase &#39;thumbs&#39;:echo $rating, &#39; thumbs up&#39;;
break;case &#39;stars&#39;:echo $rating, &#39; stars&#39;;break;}}
?>

The above routine will output:

7 thumbs up5 stars

Example #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.

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
if ((string) $movies->movie->title == &#39;PHP: Behind the Parser&#39;) {print &#39;My favorite movie.&#39;;}
echo htmlentities((string) $movies->movie->title);?>

The above routine will output:

My favorite movie.PHP: Behind the Parser

Example #7 Comparing Two Elements

Two SimpleXMLElements are considered different even if they point to the same element since PHP 5.2.0.

<?phpinclude &#39;example.php&#39;;
$movies1 = new SimpleXMLElement($xmlstr);$movies2 = new SimpleXMLElement($xmlstr);
var_dump($movies1 == $movies2); // false since PHP 5.2.0?>

The above routine will output:

bool(false)

Example #8 Using XPath

SimpleXML includes built-in support. To find all elements:

<?phpinclude &#39;example.php&#39;;
$movies = new SimpleXMLElement($xmlstr);
foreach ($movies->xpath(&#39;//character&#39;) as $character) {
echo $character->name, &#39;played by &#39;, $character->actor, PHP_EOL;}?>

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

The above routine will output:

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

Example #9 Setting values

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

<?phpinclude &#39;example.php&#39;;$movies = new SimpleXMLElement($xmlstr);
$movies->movie[0]->characters->character[0]->name = &#39;Miss Coder&#39;;
echo $movies->asXML();?>

The above routine will output:

<!--?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 ActÓr</actor>
   </character>
  </characters>
  <plot>
   So, this language. It&#39;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>

Example #10 Adding elements and attributes

Since PHP 5.1.3, SimpleXML has had the ability to easily add children and attributes.

<?phpinclude &#39;example.php&#39;;$movies = new SimpleXMLElement($xmlstr);
$character = $movies->movie[0]->characters->addChild(&#39;character&#39;);$character->addChild(&#39;name&#39;, &#39;Mr. Parser&#39;);
$character->addChild(&#39;actor&#39;, &#39;John Doe&#39;);
$rating = $movies->movie[0]->addChild(&#39;rating&#39;, &#39;PG&#39;);$rating->addAttribute(&#39;type&#39;, &#39;mpaa&#39;);
echo $movies->asXML();?>

The above routine will output ：

<!--?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 ActÓr</actor>
   </character>
  <character><name>Mr. Parser</name><actor>John Doe</actor></character></characters>
  <plot>
   So, this language. It&#39;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>

Example #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(&#39;<books><book>
<title>blah</title></book></books>&#39;);if (!$dom) {echo &#39;Error while parsing the document&#39;;exit;}
$books = simplexml_import_dom($dom);
echo $books->book[0]->title;?>

The above routine will output:

blah

Handling XML errors

Example #1 Loading broken XML string

<?php
libxml_use_internal_errors(true);
$sxe = simplexml_load_string("<?xml version=&#39;1.0&#39;><broken><xml></broken>");
if ($sxe === false) {
echo "Failed loading XML\n";
foreach(libxml_get_errors() as $error) {
echo "\t", $error->message;
}
}
?>

The above routine will output:

Failed loading XML
    Blank needed here
    parsing XML declaration: '?>' expected
    Opening and ending tag mismatch: xml line 1 and broken
    Premature end of data in tag broken line 1

3. Related functions

• simplexml_import_dom — Get a SimpleXMLElement 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

4. Related classes and member functions

SimpleXMLElement class

• ##SimpleXMLElement::addAttribute — Adds an attribute to the SimpleXML element

• SimpleXMLElement::addChild — Adds a child element to the XML node

• SimpleXMLElement::asXML — Return a well-formed XML string based on SimpleXML element

• SimpleXMLElement::attributes — Identifies an element's attributes

• SimpleXMLElement::children — Finds children of given node

• SimpleXMLElement::__construct — Creates a new SimpleXMLElement object

• SimpleXMLElement::count — Counts the children of an element

• SimpleXMLElement::getDocNamespaces — Returns namespaces declared in document

• SimpleXMLElement::getName — Gets the name of the XML element

• SimpleXMLElement ::getNamespaces — Returns namespaces used in document

• SimpleXMLElement::registerXPathNamespace — Creates a prefix/ns context for the next XPath query

• SimpleXMLElement::saveXML — 别名 SimpleXMLElement::asXML

• SimpleXMLElement::__toString — Returns the string content

• SimpleXMLElement::xpath — Runs XPath query on XML data

SimpleXMLIterator类

• SimpleXMLIterator::current — Returns the current element

• SimpleXMLIterator::getChildren — Returns the sub-elements of the current element

• SimpleXMLIterator::hasChildren — Checks whether the current element has sub elements.

• SimpleXMLIterator::key — Return current key

• SimpleXMLIterator::next — Move to next element

• SimpleXMLIterator::rewind — Rewind to the first element

• SimpleXMLIterator::valid — Check whether the current element is valid

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