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* * * 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 on what the data is. An XML file describes the structure of the data. In XML, there are no predefined tags. You must define your own tags. To learn more about XML, please visit our ( * * * ## 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 type of parser converts an 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 parsers: These parsers treat an XML document 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 the XML document rather than its structure. Because of this, event-based parsers can access data faster than tree-based parsers. Look at the following XML fragment: Jani An event-based parser reports the above XML as a sequence of three events: * Start element: from * Start CDATA section, value: Jani * End element: from The above XML example contains well-formed XML. However, this example is invalid XML because there is no associated Document Type Definition (DTD). Nevertheless, this makes no difference when using the Expat parser. Expat is a non-validating parser that ignores any DTD. As an event-based, non-validating XML parser, Expat is fast and lightweight, making it very suitable for PHP web applications. **Note:** The XML document must be well-formed; otherwise, Expat will generate an error. * * * ## Installation The XML Expat parser functions are part of PHP's core. No installation is required to use these functions. * * * ## XML File The following XML file will be used in our examples: Tove Jani Reminder Don't forget me this weekend! * * * ## Initialize XML Parser We want to initialize the XML parser in PHP, define handlers for different XML events, and then parse this 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($element_name) { case "NOTE": echo "-- Note --
"; break; case "TO": echo "To: "; break; case "FROM": echo "From: "; break; case "HEADING": echo "Heading: "; break; case "BODY": echo "Message: "; } } //Function to use at the end of an element function stop($parser,$element_name) { echo "
"; } //Function to use when finding character data function char($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! How it works: 1. Initialize the XML parser with the xml_parser_create() function 2. Create functions to handle different event handlers 3. Add the xml_set_element_handler() function to define which function to call when the parser encounters start and end tags 4. Add the xml_set_character_data_handler() function to define which function to call when the parser encounters character data 5. Parse the file "test.xml" using the xml_parse() function 6. If there are errors, add the xml_error_string() function to convert XML errors into textual descriptions 7. Call the xml_parser_free() function to free the memory allocated by the xml_parser_create() function * * * ## More Information About PHP Expat Parser For more information about PHP Expat functions, please visit our (