PHP Manual: xml_parse_into

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.

Note: xml_parse_into_struct() returns 0 for failure and 1 for success. This is not the same as FALSE and TRUE, be careful with operators such as ===.

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

Example 1. xml_parse_into_struct() example

<?php
$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 2. 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 3. parsemoldb.php - parses moldb.xml into an 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
        )

)