PHP扩展之XML操作（一）——SimpleXML

一、简介及安装

simplexml 扩展提供了一个非常简单和易于使用的工具集，能将 xml 转换成一个带有一般属性选择器和数组迭代器的对象。

此扩展需要 libxml PHP 扩展。这表示需要使用 –enable-libxml ，尽管这将隐式完成因为 libxml 是缺省开启的。

需要PHP5及以上版本。

此扩展默认为启用,编译时可通过下列选项禁用： –disable-simplexml

二、使用示例

基本使用

Example #1 Include file example.php with XML string

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<?php $xmlstr = <<<XMLMs. CoderOnlivia ActoraMr. CoderEl ActÓrSo, this language. It's like, a programming language. Or is it ascripting language? All is revealed in this thrilling horror spoofof a documentary.PHP solves all my web problems75XML;?>

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

Example #2 Getting 

movie[0]->plot;?>

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以上例程会输出：

   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.

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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 

movie->{'great-lines'}->line;?>

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以上例程会输出：

PHP solves all my web problems

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

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以上例程会输出：

Ms. Coder played by Onlivia ActoraMr. Coder played by El ActÓr

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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  'example.php';$movies = new SimpleXMLElement($xmlstr);/* Access the  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 indicescase 'thumbs':echo $rating, ' thumbs up';break;case 'stars':echo $rating, ' stars';break;}}?>

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以上例程会输出：

7 thumbs up5 stars

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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.

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

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以上例程会输出：

My favorite movie.PHP: Behind the Parser

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Example #7 Comparing Two Elements

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

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以上例程会输出：

bool(false)

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Example #8 Using XPath

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

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

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

以上例程会输出：

Ms. Coder played by Onlivia ActoraMr. Coder played by El ActÓr

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Example #9 Setting values

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

movie[0]->characters->character[0]->name = 'Miss Coder';echo $movies->asXML();?>

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以上例程会输出：

            Miss Coder    Onlivia Actora          Mr. Coder    El ActÓr          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.       PHP solves all my web problems    7  5 

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Example #10 Adding elements and attributes

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

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();?>

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以上例程会输出：

            Ms. Coder    Onlivia Actora          Mr. Coder    El ActÓr     Mr. ParserJohn Doe     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.       PHP solves all my web problems    7  5 PG

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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.

loadXML('');if (!$dom) {echo 'Error while parsing the document';exit;}$books = simplexml_import_dom($dom);echo $books->book[0]->title;?>

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以上例程会输出：

blah

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处理XML错误

Example #1 Loading broken XML string

<?php libxml_use_internal_errors(true);$sxe = simplexml_load_string("");if ($sxe === false) {echo "Failed loading XML";foreach(libxml_get_errors() as $error) {echo "", $error->message;}}?>

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以上例程会输出：

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

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三、相关函数

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

四、相关类及成员函数

SimpleXMLElement类

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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