Using PHP with XML (part 1) - Breaking It Down (Page 4 of 6 )
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.
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