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# xml_parse_into_struct

(PHP 3>= 3.0.8, PHP 4 )

xml_parse_into_struct -- Parse XML data into an array structure

## Description

int xml_parse_into_struct ( resource 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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