xml_parse_into_struct

(PHP 4, PHP 5)

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.

Parameters

parser
data
values
index

Return Values

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 ===.

Examples

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
        )

)