what is php parser

The built-in Expat parser makes it possible to process XML documents in PHP.

What is XML?

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.

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 parser: This parser converts the XML document into a tree structure. It analyzes the entire document and provides APIs to access elements of 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, not their results. Because of this, event-based parsers can access data faster than tree-based parsers.

Please look at the following XML fragment:

<from>John</from>

The event-based parser reports the above XML as a series of three events:

· Starting element: from

·Start CDATA part, value: John

·Close element: from

The above XML The examples contain well-formed XML. However, this example is invalid XML because there is no document type declaration (DTD) associated with it, and there is no embedded DTD.

Related recommendations: "php Getting Started Tutorial"

However, there is 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 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:

George
<from>John</from>
Reminder
Don't forget the meeting!

Initializing 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);
 
?>

Output of the above code:

-- Note --
To: George
From: John
Heading: Reminder
Message: Don't forget the meeting!

Explanation of working principle:

·Initialized through the xml_parser_create() function XML parser

·Create functions that match different event handlers

·Add the xml_set_element_handler() function to define when the parser encounters Which function is executed when the start and end tags are reached

·Add the xml_set_character_data_handler() function to define which function is executed when the parser encounters character data

·Parse the file "test.xml" through the xml_parse() function

·In case there is an error, add the xml_error_string() function to convert the XML error into a text description

·Call the xml_parser_free() function to release the memory allocated to the xml_parser_create() function

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