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xml_parse_into_struct

(PHP3 >= 3.0.8, PHP4 )

xml_parse_into_struct -- Parse XML data into an array structure

Description

int xml_parse_into_struct (int parser, string data, array &values, array &index)

This function parses an XML file into 2 parallel array structures, one (index) containing pointers to the location of the appropriate values in the values array. These last two parameters must be passed by reference.

Below is an example that illustrates the internal structure of the arrays being generated by the function. We use a simple note tag embeded inside a para tag, and then we parse this an print out the structures generated: 


$simple = "<para><note>simple note</note></para>";
$p = xml_parser_create();
xml_parse_into_struct($p,$simple,&$vals,&$index);
xml_parser_free($p);
echo "Index array\n";
print_r($index);
echo "\nVals array\n";
print_r($vals);

When we run that code, the output will be: 


Index array
Array
(
    [PARA] => Array
        (
            [0] => 0
            [1] => 2
        )

    [NOTE] => Array
        (
            [0] => 1
        )

)

Vals array
Array
(
    [0] => Array
        (
            [tag] => PARA
            [type] => open
            [level] => 1
        )

    [1] => Array
        (
            [tag] => NOTE
            [type] => complete
            [level] => 2
            [value] => simple note
        )

    [2] => Array
        (
            [tag] => PARA
            [type] => close
            [level] => 1
        )

)

Event-driven parsing (based on the expat library) can get complicated when you have an XML document that is complex. This function does not produce a DOM style object, but it generates structures amenable of being transversed in a tree fashion. Thus, we can create objects representing the data in the XML file easily. Let's consider the following XML file representing a small database of aminoacids information:

Example 1. moldb.xml - small database of molecular information


<?xml version="1.0"?>
<moldb>

	<molecule>
		<name>Alanine</name>
		<symbol>ala</symbol>
		<code>A</code>
		<type>hydrophobic</type>
	</molecule>

	<molecule>
		<name>Lysine</name>
		<symbol>lys</symbol>
		<code>K</code>
		<type>charged</type>
	</molecule>

</moldb>
And some code to parse the document and generate the appropriate objects:

Example 2. parsemoldb.php - parses moldb.xml into and array of molecular objects 


<?php

class AminoAcid {
	var $name;	// aa name
	var $symbol;	// three letter symbol
	var $code;	// one letter code
	var $type;	// hydrophobic, charged or neutral
	
	function AminoAcid ($aa) {
		foreach ($aa as $k=>$v)
			$this->$k = $aa[$k];
	}
}

function readDatabase($filename) {
	// read the xml database of aminoacids
	$data = implode("",file($filename));
	$parser = xml_parser_create();
	xml_parser_set_option($parser,XML_OPTION_CASE_FOLDING,0);
	xml_parser_set_option($parser,XML_OPTION_SKIP_WHITE,1);
	xml_parse_into_struct($parser,$data,&$values,&$tags);
	xml_parser_free($parser);

	// loop through the structures
	foreach ($tags as $key=>$val) {
		if ($key == "molecule") {
			$molranges = $val;
			// each contiguous pair of array entries are the 
			// lower and upper range for each molecule definition
			for ($i=0; $i < count($molranges); $i+=2) {
			    	$offset = $molranges[$i] + 1;
				$len = $molranges[$i + 1] - $offset;
				$tdb[] = parseMol(array_slice($values, $offset, $len));
			}
		} else {
			continue;
		}
	}
	return $tdb;
}

function parseMol($mvalues) {
	for ($i=0; $i < count($mvalues); $i++)
		$mol[$mvalues[$i]["tag"]] = $mvalues[$i]["value"];
	return new AminoAcid($mol);
}

$db = readDatabase("moldb.xml");
echo "** Database of AminoAcid objects:\n";
print_r($db);

?>
After executing parsemoldb.php, the variable $db contains an array of AminoAcid objects, and the output of the script confirms that: 


** Database of AminoAcid objects:
Array
(
    [0] => aminoacid Object
        (
            [name] => Alanine
            [symbol] => ala
            [code] => A
            [type] => hydrophobic
        )

    [1] => aminoacid Object
        (
            [name] => Lysine
            [symbol] => lys
            [code] => K
            [type] => charged
        )

)

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