一个简单的xml类，可以解析和生成xml文件数据

<?php
include('xml.php');
$data = XML_unserialize($xml);
?>

<?php
include('xml.php');
$xml = XML_serialize($data);
?>

<?php
###################################################################################
#
# XML Library, by Keith Devens, version 1.2b
# http://keithdevens.com/software/phpxml #
# This code is Open Source, released under terms similar to the Artistic License.
# Read the license at http://keithdevens.com/software/license #
###################################################################################

###################################################################################
# XML_unserialize: takes raw XML as a parameter (a string)
# and returns an equivalent PHP data structure
###################################################################################
function & XML_unserialize(&$xml){
$xml_parser = &new XML();
$data = &$xml_parser->parse($xml);
$xml_parser->destruct();
return $data;
}
###################################################################################
# XML_serialize: serializes any PHP data structure into XML
# Takes one parameter: the data to serialize. Must be an array.
###################################################################################
function & XML_serialize(&$data, $level = 0, $prior_key = NULL){
if($level == 0){ ob_start(); echo '<?xml version="1.0" ?>',"/n"; }
while(list($key, $value) = each($data))
if(!strpos($key, ' attr')) #if it's not an attribute
#we don't treat attributes by themselves, so for an empty element
# that has attributes you still need to set the element to NULL

if(is_array($value) and array_key_exists(0, $value)){
XML_serialize($value, $level, $key);
}else{
$tag = $prior_key ? $prior_key : $key;
echo str_repeat("/t", $level),'<',$tag;
if(array_key_exists("$key attr", $data)){ #if there's an attribute for this element
while(list($attr_name, $attr_value) = each($data["$key attr"]))
echo ' ',$attr_name,'="',htmlspecialchars($attr_value),'"';
reset($data["$key attr"]);
}

if(is_null($value)) echo " />/n";
elseif(!is_array($value)) echo '>',htmlspecialchars($value),"</$tag>/n";
else echo ">/n",XML_serialize($value, $level+1),str_repeat("/t", $level),"</$tag>/n";
}
reset($data);
if($level == 0){ $str = &ob_get_contents(); ob_end_clean(); return $str; }
}
###################################################################################
# XML class: utility class to be used with PHP's XML handling functions
###################################################################################
class XML{
var $parser;   #a reference to the XML parser
var $document; #the entire XML structure built up so far
var $parent;   #a pointer to the current parent - the parent will be an array
var $stack;    #a stack of the most recent parent at each nesting level
var $last_opened_tag; #keeps track of the last tag opened.

function XML(){
$this->parser = &xml_parser_create();
xml_parser_set_option(&$this->parser, XML_OPTION_CASE_FOLDING, false);
xml_set_object(&$this->parser, &$this);
xml_set_element_handler(&$this->parser, 'open','close');
xml_set_character_data_handler(&$this->parser, 'data');
}
function destruct(){ xml_parser_free(&$this->parser); }
function & parse(&$data){
$this->document = array();
$this->stack    = array();
$this->parent   = &$this->document;
return xml_parse(&$this->parser, &$data, true) ? $this->document : NULL;
}
function open(&$parser, $tag, $attributes){
$this->data = ''; #stores temporary cdata
$this->last_opened_tag = $tag;
if(is_array($this->parent) and array_key_exists($tag,$this->parent)){ #if you've seen this tag before
if(is_array($this->parent[$tag]) and array_key_exists(0,$this->parent[$tag])){ #if the keys are numeric
#this is the third or later instance of $tag we've come across
$key = count_numeric_items($this->parent[$tag]);
}else{
#this is the second instance of $tag that we've seen. shift around
if(array_key_exists("$tag attr",$this->parent)){
$arr = array('0 attr'=>&$this->parent["$tag attr"], &$this->parent[$tag]);
unset($this->parent["$tag attr"]);
}else{
$arr = array(&$this->parent[$tag]);
}
$this->parent[$tag] = &$arr;
$key = 1;
}
$this->parent = &$this->parent[$tag];
}else{
$key = $tag;
}
if($attributes) $this->parent["$key attr"] = $attributes;
$this->parent  = &$this->parent[$key];
$this->stack[] = &$this->parent;
}
function data(&$parser, $data){
if($this->last_opened_tag != NULL) #you don't need to store whitespace in between tags
$this->data .= $data;
}
function close(&$parser, $tag){
if($this->last_opened_tag == $tag){
$this->parent = $this->data;
$this->last_opened_tag = NULL;
}
array_pop($this->stack);
if($this->stack) $this->parent = &$this->stack[count($this->stack)-1];
}
}
function count_numeric_items(&$array){
return is_array($array) ? count(array_filter(array_keys($array), 'is_numeric')) : 0;
}
?>