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         )  )