How to use XML functions in PHP

XML is a commonly used data exchange format, and PHP has many functions and classes for processing XML data. You can use them to easily read, parse, create and modify XML documents. This article will introduce how to use XML functions in PHP.

1. XML parsing function

There are three commonly used XML parsing functions in PHP: simplexml_load_file(), simplexml_load_string() and xml_parse(), which can be used to read and Parse XML documents.

simplexml_load_file() function takes an XML document as a parameter and returns a simple XML object. For example:

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

The $xml object can operate XML nodes like an array, for example:

echo $xml- >book[0]->title; // Output the title value of the first book node

simplexml_load_string() function is similar to the simplexml_load_file() function. You can use an XML string as a parameter and return a simple XML object.

xml_parse() function can parse the nodes and attributes of the XML document one by one and trigger the callback function. For example:

function startElement($parser, $name, $attrs) {
echo "Start node $name
";
}

function endElement($parser , $name) {
echo "End node $name
";
}

$parser = xml_parser_create();
xml_set_element_handler($parser, "startElement", "endElement ");

$xml = file_get_contents("test.xml");
xml_parse($parser, $xml);

The xml_parse() function needs to be created using the xml_parser_create() function parser, and use the xml_set_element_handler() function to set the node start and end callback functions.

2. XMLWriter class

XMLWriter is a class in PHP used to create XML documents. It provides a series of methods to build XML documents, such as startDocument(), endDocument(), startElement(), endElement(), writeElement(), writeAttribute(), etc.

The following is an example of using the XMLWriter class to create an XML document:

$xmlWriter = new XMLWriter();
$xmlWriter->openURI('output.xml');
$xmlWriter->startDocument('1.0', 'UTF-8'); // Set XML version and encoding
$xmlWriter->startElement('root');
$xmlWriter-> writeElement('book', 'Getting Started with PHP');
$xmlWriter->writeElement('price', '19.99');
$xmlWriter->endElement(); // End the root node
$xmlWriter->endDocument(); //End document

In the above example, we used the XMLWriter class to create an XML document named output.xml, and used the startDocument() function to set the XML Version and encoding, use the startElement() and endElement() functions to create the root node, and use the writeElement() function to write the values of the book and price nodes.

3. DOM extension

DOM extension in PHP provides a flexible way to process XML documents. You can also use XPath expressions to query XML documents, modify nodes and attributes, etc. .

The following is an example of using DOM extensions to read and modify XML documents:

$dom = new DOMDocument();
$dom->load('test.xml' );
$books = $dom->getElementsByTagName('book');
foreach ($books as $book) {
$title = $book->getElementsByTagName('title')- >item(0);
$title->nodeValue = 'PHP Advanced Guide';
}
$dom->save('test.xml');

In the above example, we use the DOMDocument class to load the XML document, use the getElementsByTagName() function to obtain the node array, use the item() function to obtain a single node, and use the nodeValue attribute to modify the node value, and finally save the modified XML document.

Summary

PHP provides a variety of functions and classes for processing XML data, making it very convenient to operate XML documents in PHP. Developers can choose different XML processing methods based on actual needs and personal preferences.

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