PHP XML Expat parser
The built-in Expat parser makes it possible to process XML documents in PHP .
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.
What is Expat?
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 parsers: 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: 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.
Look at the following XML fragment:
<from>Jani</from>
The event-based parser reports the above XML as a series of three events :
· Starting element: from
· Starting CDATA section, value: Jani
· Closing element: from
The XML example above contains the form Good 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.
Installation
The XML Expat parser function is an integral part of PHP core. No installation is required to use these functions.
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>
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
<?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);
?>The above code will output:
-- Note --
To: Tove
From: Jani
Heading: Reminder
Message: Don't forget me this weekend!
Working principle:
1. Initialize the XML parser through the xml_parser_create() function
2. Create an XML parser that matches different event handlers Function
3. Add xml_set_element_handler() function to define which function is executed when the parser encounters the start and end tags
4. Add xml_set_character_data_handler() function to define when the parser encounters the start and end tags Which function is executed when character data is encountered
5. Use the xml_parse() function to parse the file "test.xml"
6. In case of an error, add the xml_error_string() function to parse the XML Convert the error to a text description
7. Call the xml_parser_free() function to release the memory allocated to the xml_parser_create() function
PHP XML Parser Introduction
The XML function allows you to parse an XML document but not validate it.
XML is a data format used for the exchange of standard structured documents. You can find more information about XML in our php.cn.
This extension uses the Expat XML parser.
Expat is an event-based parser that treats XML documents as a series of events. When an event occurs, it calls a specified function to handle it.
Expat is a validation-free parser that ignores any DTD linked to the document. However, if the document is not in good form, it will end up with an error message.
Because it is an event-based, validation-free parser, Expat is fast and suitable for web applications.
The XML parser function allows you to create an XML parser and define handlers for XML events.
Installation
The XML Parser function is an integral part of the PHP core. No installation is required to use these functions.
PHP XML Parser Function
PHP: Indicates the earliest PHP version that supports this function.
PHP XML Parser Constants
