1. What is XML
XML is used to describe data, and its focus is 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.
2. What is Expat
To read and update - create and process - an XML document, you need XML parser.
There are two basic types of XML parsers:
Tree-based parsers: This parser converts the XML document 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: Treat XML documents 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 For a series of three events: leaving the stack inside the individual
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, otherwise Expat will generate an error.
3. Installation
The XML Expat parser function is an integral part of the PHP core. No installation is required to use these functions.
4. XML file
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>
#5. Initialize the XML parser
We need to initialize the XML parser in PHP, define handlers for different XML events, and then parse the XML file.
Example:
The code is as follows:
<?php
//Initialize the XML parser
$parser=xml_parser_create();
//Function to use at the start of an element
function start($parser,$element_name,$element_attrs)
{
switch($element_name)
{
case "NOTE":
echo "-- Note --<br>";
break;
case "TO":
echo "To: ";
break;
case "FROM":
echo "From: ";
break;
case "HEADING":
echo "Heading: ";
break;
case "BODY":
echo "Message: ";
}
}
//Function to use at the end of an element
function stop($parser,$element_name)
{
echo "<br>";
}
//Function to use when finding character data
function char($parser,$data)
{
echo $data;
}
//Specify element handler
xml_set_element_handler($parser,"start","stop");
//Specify data handler
xml_set_character_data_handler($parser,"char");
//Open XML file
$fp=fopen("test.xml","r");
//Read data
while ($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 parser
xml_parser_free($parser);
?>Note: The test.xml file here is the content of the fourth part of this section
6. More information about PHP Expat parser
For more information about PHP Expat function, please visit our PHP XML Parser Reference book.
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