xml_set_element_handler()

(PHP 4, PHP 5, PHP 7)

建立起始和终止元素处理器

说明

xml_set_element_handler (resource $parser,callable $start_element_handler,callable $end_element_handler) : bool

为$parser参数指定的 XML 解析器建立元素处理器函数。参数$start_element_handler和$end_element_handler为表示函数名称的字符串，这些函数必须在为$parser指定的解析器调用 xml_parse() 函数时已存在。

参数

$parser

XML 解析器的引用，用于建立起始和终止元素处理器。

$start_element_handler

由$start_element_handler参数命名的函数名必须接受三个参数：

start_element_handler (resource $parser,string $name,array $attribs)

$parser: 第一个参数 parser 为指向要调用处理器的 XML 解析器的指针。
$name: 第二个参数$name为该处理器为之被调用的元素名。如果大小写折叠（case-folding）对该解析器有效，元素名将用大写字母表示。
$attribs: 第三个参数$attribs为一个包含有对应元素的属性的数组（如果该元素有属性）。数组元素的下标为属性名，元素的值即为属性的值。属性名将以和元素名同样的标准进行大小写折叠（case-folded），其值不进行大小写折叠。属性的原始顺序将会被参数保留，用 each() 函数遍历$attribs时，该数组下表的顺序和属性的顺序相同。

Note: 除了函数名，含有对象引用的数组和方法名也可以作为参数。

$end_element_handler

由$end_element_handler参数命名的函数名必须接受两个参数：

end_element_handler (resource $parser,string $name)

$parser: 第一个参数 parser 为指向要调用处理器的 XML 解析器的指针。
$name: 第二个参数$name为该处理器为之被调用的元素名。如果大小写折叠（case-folding）对该解析器有效，元素名将用大写字母表示。

如果处理器函数名被设置为空字符串或者 FALSE，则该有问题的处理器将被屏蔽。

返回值

成功时返回 TRUE，或者在失败时返回 FALSE。

This documentation is somewhat awry. I know it's been said many times before, but it bears repeating...
If using PHP4, you may be required to use xml_set_object() instead of calling any of the xml_set_*_handler() functions with a two-item array. It will work fine on PHP5, but move the same code to PHP4 and it will create one copie of $this (even if you use &$this) for each handler you set!
<?php
// This code will fail mysteriously on PHP4.
$this->parser = xml_parser_create();
xml_set_element_handler(
      $this->parser,
      array(&$this,"start_tag"),
      array(&$this,"end_tag")
    );
    xml_set_character_data_handler(
      $this->parser,
      array(&$this,"tag_data")
    );
?>
<?php
// This code will work on PHP4.
$this->parser = xml_parser_create();
xml_set_object($this->parser,&$this); 
xml_set_element_handler(
      $this->parser,
      "start_tag",
      "end_tag"
    );
    xml_set_character_data_handler(
      $this->parser,
      "tag_data"
    );
?>

<html> 
 <head> 
  <title>SAX Demonstration</title> 
  <META HTTP-EQUIV='Content-type' CONTENT='text/html; charset=euc-kr'> 
 </head> 
 <body> 
  <h1>RSS </h1> 
  
   <?php 
   $file = "data.xml"; 
   
   $currentTag = ""; 
   $currentAttribs = ""; 
   function startElement($parser, $name, $attribs) 
   { 
     global $currentTag, $currentAttribs; 
     $currentTag = $name; 
  
     $currentAttribs = $attribs; 
     switch ($name) { 
     
     default: 
       echo("<b>&lt$name&gt</b><br>"); 
       break; 
     } 
   } 
   function endElement($parser, $name) 
   { 
     global $currentTag; 
     switch ($name) { 
     default: 
       echo("<br><b>&lt/$name&gt</b><br><br>"); 
       break; 
     } 
     $currentTag = ""; 
     $currentAttribs = ""; 
   } 
   function characterData($parser, $data) 
   { 
     global $currentTag; 
     switch ($currentTag) { 
     case "link": 
       echo("<a href=\"$data\">$data</a>\n"); 
       break; 
     case "title": 
       echo("title : $data"); 
       break; 
     default: 
       echo($data); 
       break; 
     } 
   } 
   $xmlParser = xml_parser_create(); 
  
   $caseFold = xml_parser_get_option($xmlParser, 
                    XML_OPTION_CASE_FOLDING); 
  
   $targetEncoding = xml_parser_get_option($xmlParser, 
                       XML_OPTION_TARGET_ENCODING); 
   if ($caseFold == 1) { 
     xml_parser_set_option($xmlParser, XML_OPTION_CASE_FOLDING, false); 
   } 
   xml_set_element_handler($xmlParser, "startElement", "endElement"); 
   xml_set_character_data_handler($xmlParser, "characterData"); 
   if (!($fp = fopen($file, "r"))) { 
     die("Cannot open XML data file: $file"); 
   } 
   while ($data = fread($fp, 4096)) { 
     if (!xml_parse($xmlParser, $data, feof($fp))) { 
       die(sprintf("XML error: %s at line %d", 
             xml_error_string(xml_get_error_code($xmlParser)), 
             xml_get_current_line_number($xmlParser))); 
       xml_parser_free($xmlParser); 
     } 
   } 
   xml_parser_free($xmlParser); 
   ?> 
  </table> 
 </body> 
</html>

In response to landb at mail dot net...
As the notes mention, you can pass an array that contains the reference to an object and a method name when you need... so you can call methods in your own class as handlers like this:
xml_set_element_handler($parser, array($this,"_startElement"), array($this,"_endElement"));
Hope it helps...

My 25 cents. This example show how to parse a XML in a associative array tree.
<?php
$file = "flow/flow.xml";
$depth = 0;
$tree = array();
$tree['name'] = "root"; 
$stack[count($stack)] = &$tree;
function startElement($parser, $name, $attrs) {
  global $depth;
  global $stack;
  global $tree;
  
  $element = array();
  $element['name'] = $name;
  foreach ($attrs as $key => $value) { 
    //echo $key."=".$value;
    $element[$key]=$value;
  }
  $last = &$stack[count($stack)-1];
  $last[count($last)-1] = &$element;
  $stack[count($stack)] = &$element;
  $depth++;
}
function endElement($parser, $name) {
  global $depth;
  global $stack;
  array_pop($stack);
  $depth--;
}
$xml_parser = xml_parser_create();
xml_set_element_handler($xml_parser, "startElement", "endElement");
if (!($fp = fopen($file, "r"))) {
  die("could not open XML input");
}
while ($data = fread($fp, 4096)) {
  if (!xml_parse($xml_parser, $data, feof($fp))) {
    die(sprintf("XML error: %s at line %d",
          xml_error_string(xml_get_error_code($xml_parser)),
          xml_get_current_line_number($xml_parser)));
  }
}
xml_parser_free($xml_parser);
$tree = $stack[0][0];
echo "<pre>";
print_r($tree);
echo "</pre>";

I modified the previous script, so that it is associative. I find it more useful that way. BTW I prefer strtolower() things, but that's not mandatory at all.
<?php
$file = "data.xml";
$depth = 0;
$tree = array();
$tree['name'] = "root";
$stack[] = &$tree;
function startElement($parser, $name, $attrs) {
  global $depth;
  global $stack;
  global $tree;
 
  $element = array();
  foreach ($attrs as $key => $value) {
    $element[strtolower($key)]=$value;
  }
  end($stack);
  $stack[key($stack)][strtolower($name)] = &$element;
  $stack[strtolower($name)] = &$element;
  
  $depth++;
}
function endElement($parser, $name) {
  global $depth;
  global $stack;
  array_pop($stack);
  $depth--;
}
$xml_parser = xml_parser_create();
xml_set_element_handler($xml_parser, "startElement", "endElement");
if (!($fp = fopen($file, "r"))) {
  die("could not open XML input");
}
while ($data = fread($fp, 4096)) {
  if (!xml_parse($xml_parser, $data, feof($fp))) {
    die(sprintf("XML error: %s at line %d",
          xml_error_string(xml_get_error_code($xml_parser)),
          xml_get_current_line_number($xml_parser)));
  }
}
xml_parser_free($xml_parser);
$tree = end(end($stack));
echo "<pre>";
print_r($tree);
echo "</pre>";
?>

I ran into the same problem with 'ibjoel at hotmail dot com' in regards to self-closing tags, and found that the script that he/she wrote did not work as I expected.
I played around with some of php's functions and examples and compiled something, which may not be the neatest solution, but it works for the data that 'ibjoel at hotmail dot com' provided.
The data needs to be read from a file though, so the fp can be utilised. It still uses the xml_get_current_byte_index(resource parser) trick, but this time, I check for the last 2 character before the index and test if it's "/>".
<?php
/* myxmltest.xml:
<normal_tag>
 <self_close_tag />
   data
 <normal_tag>data
   <self_close_tag attr="value" />
 </normal_tag>
   data
 <normal_tag></normal_tag>
</normal_tag>
*/
//## Global Variables ##//
$file = "myxmltest.xml";
$character_data_on = false;
$tag_complete = true;
function startElement($parser, $name, $attrs) 
{
  global $character_data_on;
  global $tag_complete;
  
  echo "&lt;<font color=\"#0000cc\">$name</font>";
  //## Print the attributes ##//
  if (sizeof($attrs)) {
    while (list($k, $v) = each($attrs)) {
      echo " <font color=\"#009900\">$k</font>=\"<font 
          color=\"#990000\">$v</font>\"";
    }
  }
  //## Tag is still still incomplete,
  //## will be completed at either endElement or characterData ##//
  $tag_complete = false;
  $character_data_on = false;
}
function endElement($parser, $name) 
{
  global $fp;
  global $character_data_on;
  global $tag_complete;
  
  //#### Test for self-closing tag ####//
  //## xml_get_current_byte_index(resource parser) when run in this
  //## function, gives the index at (indicated by *):
  //##  for self closing tag: <br />*
  //##  for individual closing tag: <div>character data*</div>
  //## So to test for self-closing tag, we can just test for the last 2 
  //## characters from the index
  //###################################//
  
  if (!$character_data_on) {
    //## Record current fp position ##//
    $temp_fp = ftell($fp);
    
    //## Point fp to 2 bytes before the end element byte index ##//
    $end_element_byte_index = xml_get_current_byte_index($parser);
    fseek($fp,$end_element_byte_index-2);
    
    //## Gets the last 2 characters before the end element byte index ##//
    $validator = fgets($fp, 3);
    
    //## Restore fp position ##//
    fseek($fp,$temp_fp);
    
    //## If the last 2 character is "/>" ##//
    if ($validator=="/>") {
      //// Complete the self-closing tag ////
      echo " /&gt";
      //// Otherwise it is an individual closing tag ////
    } else echo "&gt&lt/<font color=\"#0000cc\">$name</font>&gt";
    $tag_complete = true;
  } else echo "&lt/<font color=\"#0000cc\">$name</font>&gt";
  
  $character_data_on = false;
}
function characterData($parser, $data) 
{
  global $character_data_on;
  global $tag_complete;
  
  if ((!$character_data_on)&&(!$tag_complete)) {
    echo "&gt";
    $tag_complete = true;
  }
  echo "<b>$data</b>"; 
  $character_data_on = true;
}
$xml_parser = xml_parser_create();
xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, false);
xml_set_element_handler($xml_parser, "startElement", "endElement");
xml_set_character_data_handler($xml_parser, "characterData");
if (!($fp = fopen($file, "r"))) {
  die("could not open XML input");
}
echo "<pre>";
while ($file_content = fread($fp, 4096)) {
  if (!xml_parse($xml_parser, $file_content, feof($fp))) {
    die(sprintf("XML error: %s at line %d",
 &nbnbsp;         xml_error_string(xml_get_error_code($xml_parser)),
          xml_get_current_line_number($xml_parser)));
  }
}
echo "</pre>";
xml_parser_free($xml_parser);
?>

If you are using a class for xml parsing, and want to check the return value of xml_set_element_handler in case it fails, you must do this outside of the class's constructor. Inside the constructor, PHP-4.0.5 will die.
Basically, put all your xml initialisation code in another function of the class, and keep it out of the constructor.

Example below (BadParser) works fine with some changes.
xml_set_element_handler ( $parser, array ( &$this, 'tagStart' ), array ( &$this, 'tagEnd' ) );
xml_set_character_data_handler ( $parser, array ( &$this, 'tagContent' ) );

The method that 'ibjoel at hotmail dot com' have described requires libxml2 as the xml parser, it does not work with expat. For a brief explanation, see xml_get_current_byte_index.

I noticed that in the example below, and all the examples I've seen on this site for viewing xml in html, the look of self closing tags such as <br /> are not preserved. The parser cannot distinguish between <tag /> and <tag></tag>, and if your start and end element functions are like these examples, both instances will be output with both an indvidual start and end tag. I needed to preserve self-closing tags and it took me a while to figure out this work around. Hope this helps someone...
 
The start tag is left open, and then completed by it's first child, the next start tag or its end tag. The end tag will complete with " />", or </tag> depending on the number of bytes between the start and end tags in the parsed data.
<?php
//$data=filepath or string
$data=<<<DATA
<normal_tag>
 <self_close_tag />
   data
 <normal_tag>data
   <self_close_tag attr="value" />
 </normal_tag>
   data
 <normal_tag></normal_tag>
</normal_tag>
DATA;
function startElement($parser, $name, $attrs)
{
    xml_set_character_data_handler($parser, "characterData");
    global $first_child, $start_byte;
    if($first_child)     //close start tag if neccessary
        echo "><br />";
    $first_child=true;
    $start_byte=xml_get_current_byte_index ($parser);
    if(count($attrs)>=1){
        foreach($attrs as $x=>$y){
            $attr_string .= " $x=\"$y\"";
        }
    }
    echo htmlentities("<{$name}{$attr_string}"); //unclosed starttag
}
function endElement($parser, $name)
{
    global $first_child, $start_byte;
    $byte=xml_get_current_byte_index ($parser);
    if($byte-$start_byte>2){      //if end tag is more than 2 bytes from start tag
        if($first_child)     //close start tag if neccessary
            echo "><br />";
        echo htmlentities("</{$name}>")."<br />"; //individual end tag
    }else
        echo " /><br />"; // self closing tag
    $first_child=false;
}
function characterData($parser, $data)
{
    global $first_child;
    if($first_child) //if $data is first child, close start tag
        echo "><br />";
    if($data=trim($data))
        echo "<font color='blue'>$data</font><br />";
    $first_child=false;
}
function ParseData($data)
{
    $xml_parser = xml_parser_create();
    xml_set_element_handler($xml_parser, "startElement", "endElement");
    xml_parser_set_option($xml_parser,XML_OPTION_CASE_FOLDING,0);
    if(is_file($data))
    {
        if (!($fp = fopen($file, "r"))) {
            die("could not open XML input");
        }
        while ($data = fread($fp, 4096)) {
            if (!xml_parse($xml_parser, $data, feof($fp))) {
                $error=xml_error_string(xml_get_error_code($xml_parser));
                $line=xml_get_current_line_number($xml_parser);
                die(sprintf("XML error: %s at line %d",$error,$line));
            }
        }
    }else{
        if (!xml_parse($xml_parser, $data, 1)) {
                $error=xml_error_string(xml_get_error_code($xml_parser));
                $line=xml_get_current_line_number($xml_parser);
                die(sprintf("XML error: %s at line %d",$error,$line));
        }
    }
    
    xml_parser_free($xml_parser);
}
ParseData($data);
?>

It seems that the tag handlers don't block on one another (the end handler is called whether or not the begin handler has finished). this can put you in a tight spot if you don't realize it while planning your app.

It seems that characterData() gets characters in chuncks of 1024; therefore if you have string of characters between you tags that is longer than 1024 then characterData() will be called more that once for single pair of tags. I don't know if this feature(bug?) is documented anywhere, I just wanted to warn everyone about this; it had tripped me. I use php 4.3.10 on Linux.

Here is another example of detecting empty elements. I works with libxml2. Note that it handles buffer boundaries.
<?php
$depth = 0; //current depth, used for pretty printing
$empty = false; //whether the tag is empty
$offset = 0; //the index of the start of the current buffer within the stream
function tagStart($parser, $name, array $attribs) {
  global $depth, $empty, $data, $offset, $lastchar;
  $idx = xml_get_current_byte_index($parser);
  /* xml_get_current_byte_index returns index within the streams and not
    within the buffer.*/
  
  /* Check if the index is within the buffer. */
  if (isset($data[$idx - $offset])) {
    $c = $data[$idx - $offset];
  } else {
    /* If it isn't simple use the last character of the buffer. */
    $c = $lastchar;
  }
  $empty = $c == '/';
  echo str_repeat("\t", $depth), "<$name", ($empty ? '/>' : '>'), "\n";
  if (!$empty) ++$depth;
}
function tagEnd($parser, $name) {
  global $depth, $empty;
  if (!$empty) {
    --$depth;
    echo str_repeat("\t", $depth), "</$name>\n";
  } else {
    $empty = false;
  }
}
$parser = xml_parser_create();
xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, false);
xml_set_element_handler($parser, 'tagStart', 'tagEnd');
$data1 = '
<test>
  <empty att="3" />
  <nocontent></nocontent>
  <content>
    <empty/>
    <empty/>
  </content>
  <empty/';
$data2 = '>
  <empty att="5" />
</test>
';
$data = &$data1;
$length = strlen($data1);
$lastchar = $data[$length-1];
xml_parse($parser, $data1);
$offset .= $length;
$data = &$data2;
xml_parse($parser, $data2);

You CAN use classes to parse XML. Just take a look at the following function:
xml_set_object

In response to aw at avatartechnology dot com...
In response to landb at mail dot net...
When your functions are in an object:
Careful ! Don't forget to add: & (reference) to your parameters.
xml_set_element_handler($parser, array(&$this,"_startElement"), array(&$this,"_endElement"));
--> xmlparse will work on your object (good).
instead of:
xml_set_element_handler($parser, array($this,"_startElement"), array($this,"_endElement"));
---> xmlparse will work on a COPY of your object (often bad)
Vin-s
(sorry for my english)