The built-in Expat parser makes it possible to process XML documents in PHP.
XML is used to describe data, with the focus being on what the data is. XML files describe the structure of data.
In XML, there are no predefined tags. You must define your own tags.
To learn more about XML, visit our XML tutorial.
To read and update - create and process - an XML document, you need an XML parser.
There are two basic types of XML parsers:
Tree-based parser: This parser converts XML documents into a tree structure. It analyzes the entire document and provides access to elements in the tree, such as the Document Object Model (DOM).
Event-based parser: Treats an XML document as a series of events. When a specific event occurs, the parser calls a function to handle it.
The Expat parser is an event-based parser.
Event-based parsers focus on the content of XML documents rather than their structure. Because of this, event-based parsers are able to access data faster than tree-based parsers.
Please see the following XML fragment:
<from>Jani</from>
The event-based parser reports the above XML as a sequence of three events:
Start element: from
Start CDATA section, value: Jani
Close element: from
The XML example above contains well-formed XML. However, this instance is invalid XML because there is no document type declaration (DTD) associated with it.
However, this makes no difference when using the Expat parser. Expat is a parser that does not check validity and ignores any DTD.
As an event-based, non-validated XML parser, Expat is fast and lightweight, making it ideal for PHP Web applications.
Note: The XML document must be well formed or Expat will generate an error.
The XML Expat parser function is an integral part of PHP core. No installation is required to use these functions.
The following XML file will be used in our example:
<?xml version="1.0" encoding="ISO-8859-1"?><note><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don 't forget me this weekend!</body></note>
We need to initialize the XML parser in PHP, define handlers for different XML events, and then parse the XML file.
<?php//Initialize the XML parser$parser=xml_parser_create();//Function to use at the start of an elementfunction start($parser,$element_name,$element_attrs) { switch($element_name) { case "NOTE": echo "-- Note --<br>"; break; case "TO": echo "To: "; break; case "FROM": echo "From: "; break; case "HEADING": echo "Heading: "; break; case "BODY": echo "Message: "; } }//Function to use at the end of an elementfunction stop($parser,$element_name) { echo "<br> "; }//Function to use when finding character datafunction char($parser,$data) { echo $data; }//Specify element handlerxml_set_element_handler($parser,"start","stop");//Specify data handlerxml_set_character_data_handler($parser,"char");//Open XML file$fp=fopen("test.xml","r");/ /Read datawhile ($data=fread($fp,4096)) { xml_parse($parser,$data,feof($fp)) or die (sprintf("XML Error: %s at line %d", xml_error_string(xml_get_error_code($parser)), xml_get_current_line_number($parser))); }/ /Free the XML parserxml_parser_free($parser);?>The above code will output:
-- Note --To: ToveFrom: JaniHeading: ReminderMessage: Don't forget me this weekend!
How it works:
Initialize the XML parser through the xml_parser_create() function
Create functions that work with different event handlers
Add xml_set_element_handler() function to define which function to execute when the parser encounters the opening and closing tags
Add xml_set_character_data_handler() function to define which function to execute when the parser encounters character data
Parse the file "test.xml" through the xml_parse() function
In case of errors, add xml_error_string() function to convert XML errors into text descriptions
Call the xml_parser_free() function to release the memory allocated to the xml_parser_create() function
To learn more about the PHP Expat function, visit our PHP XML Parser reference manual.