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PHP XML Expat Parser  


PHP XML Expat Parser

PHP XML Expat Parser

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

The XML Expat Parser

The Expat parser is an event-based parser.

Look at the following XML fraction:

<from>Jani</from>

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

  • Start element: from
  • Start CDATA section, value: Jani
  • Close element: from

The XML Expat Parser functions are part of the PHP core. There is no installation needed to use these functions.

The XML File

The XML file "note.xml" will be used in the example below:

<?xml version="1.0" encoding="UTF-8"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

Initializing the XML Expat Parser

We want to initialize the XML Expat 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("note.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);
?>

 

Example explained:

  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 "note.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

 

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