Do you know what XML Expat is? How does he define it?

The previous article introduced to you "How to use PHP MySQL for data connection? 》, this article continues to introduce to you about PHP XML Expat. I wonder if you are interested in XML? Then let’s go and see it together! ! !

What is XML:

XML is used to describe data, and its focus is what the data is. XML files describe the structure of data. PHP XML EXPAT.

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, the user needs an 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>

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, 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:

Tove
<from>Jani</from>
Reminder
Don't forget me this weekend!

Initializing the XML parser

us To initialize the XML parser in PHP, define handlers for different XML events, and then parse the XML file.

The specific 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);
?>

The above code will output:

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