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Breaking It Down - XML

By separating content from presentation, XML offers Web developers a powerful alternative to traditional HTML technology...and when you combine that with PHP, you have a truly compelling new set of tools. In this article, find out how PHP's SAX parser can be used to parse XML data and generate HTML Web pages.

TABLE OF CONTENTS:
  1. Using PHP with XML (part 1)
  2. Getting Down To Business
  3. Let's Talk About SAX
  4. Breaking It Down
  5. Call Me Back
  6. What's For Dinner?
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 25
June 18, 2001

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The first order of business is to initialize the XML parser, and set up the callback functions.

<? // data file $file = "library.xml"; // initialize parser $xml_parser = xml_parser_create(); // set callback functions xml_set_element_handler($xml_parser, "startElement", "endElement"); xml_set_character_data_handler($xml_parser, "characterData"); // open XML file if (!($fp = fopen($file, "r"))) { die("Cannot locate XML data file: $file"); } // read and parse data while ($data = fread($fp, 4096)) { // error handler if (!xml_parse($xml_parser, $data, feof($fp))) { die(sprintf("XML error: %s at line %d", xml_error_string(xml_get_error_code($xml_parser)), xml_get_current_line_number($xml_parser))); } } // clean up xml_parser_free($xml_parser); ?>
The xml_parser_create() function is used to initialize the parser, and assign it to a handle, which may be used by subsequent function calls. Once the parser is initialized, the next step is to specify callback functions for the different types of tags.

The xml_set_element_handler() function is used to specify the functions to be executed when the parser encounters the opening and closing tags of an element - in this case, the functions startElement() and endElement() respectively. The xml_set_character_data_handler() function specifies the function to be called when the parser encounters character data - in this case, characterData().

In addition, PHP also offers the xml_set_processing_instruction_handler(), for processing instructions; xml_set_unparsed_entity_decl_handler(), for unparsed entities; xml_set_external_entity_ref_handler(), for external entities; xml_set_notation_decl_handler(), for notation declarations; and xml_set_default_handler(), for all other entities within a document. In case you don't know what any of these are, don't worry about it - I'm not planning to use any of them here.

The next step in the script above is to open the XML file (as defined in the $file variable), read it and parse it via the xml_parse() function. The xml_parse() function will call the appropriate handling function each time it encounters a specific tag type. Once the document has been completely parsed, the xml_parser_free() function is called to free used memory and clean things up.

Errors can be displayed by means of the xml_error_string() function, which returns a description of the error encountered by the parser. Additional functions like xml_get_error_code(), xml_get_current_line_number(), xml_get_current_column_number(), and xml_get_current_byte_index() provide some additional information on the error.

 
 
>>> More XML Articles          >>> More By icarus, (c) Melonfire
 

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