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PHP XML Expat Parser
Posted by jujur
on
5:43 AM
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
to focus on what data is. An XML file describes the structure of the data.In XML, no tags are predefined. You must define your own tags.
If you want to learn more about XML, please visit our XML tutorial.
What is Expat?
To read and update - create and
manipulate - an XML document, you will need an XML parser.There are two basic types of XML parsers:
- Tree-based parser: This parser
transforms an XML document into a tree structure. It analyzes the whole
document, and provides access to the tree elements. e.g. the Document
Object Model (DOM)
- Event-based parser: Views an XML
document as a series of events. When a specific event occurs, it calls a
function to handle it
Event-based parsers focus on the content of the XML documents, not its structure. Because of this, event based parsers can access data faster than Tree-based parsers.
Look at the following XML fraction:
<from>Jani</from>
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- Start element: from
- Start CDATA section, value: Jani
- Close element: from
However, this makes no difference when using the Expat parser. Expat is a non-validating parser, and ignores any DTDs.
As an event-based, non-validating XML parser, Expat is fast and small, and a perfect match for PHP web applications.
Note: XML documents must be well-formed or Expat will generate an error.
Installation
The XML Expat parser functions are
part of the PHP core. There is no installation needed to use these functions.
An XML File
The XML file below 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>
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Initializing the XML Parser
We want to initialize the XML
parser in PHP, define some 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);
?>
|
-- Note --
To: Tove
From: Jani
Heading: Reminder
Message: Don't forget me this weekend!
|
1. Initialize
the XML parser with the xml_parser_create() function
2. Create
functions to use with the different event handlers
3. Add the
xml_set_element_handler() function to specify which function will be executed
when the parser encounters the opening and closing tags
4. Add the
xml_set_character_data_handler() function to specify which function will
execute when the parser encounters character data
5. Parse
the file "test.xml" with the xml_parse() function
6. In case
of an error, add xml_error_string() function to convert an XML error to a
textual description
7. Call the
xml_parser_free() function to release the memory allocated with the
xml_parser_create() function
More PHP Expat Parser
For more information about the PHP
Expat functions, visit our PHP XML Parser Reference.
