XMLReader::read()

(PHP 5 >= 5.1.0, PHP 7)

Move to next node in document

说明

publicXMLReader::read(void): bool

Moves cursor to the next node in the document.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

参见

• XMLReader::moveToElement() Position cursor on the parent Element of current Attribute
• XMLReader::moveToAttribute() Move cursor to a named attribute
• XMLReader::next() Move cursor to next node skipping all subtrees

libxml2 contains much more useful method readString() that will read and return whole text content of element. You can call it after receiving start tag (XMLReader::ELEMENT). You can use this PHP code to emulate this method until PHP will directly call underlying libxml2 implementation.
<?php
class XMLReader2 extends XMLReader
{
 function readString()
 {
    $depth = 1;
    $text = "";
    while ($this->read() && $depth != 0)
    {
      if (in_array($this->nodeType, array(XMLReader::TEXT, XMLReader::CDATA, XMLReader::WHITESPACE, XMLReader::SIGNIFICANT_WHITESPACE)))
        $text .= $this->value;
      if ($this->nodeType == XMLReader::ELEMENT) $depth++;
      if ($this->nodeType == XMLReader::END_ELEMENT) $depth--;
    }
    return $text;
  }
}
?>
Just use XMLReader2 instead of XMLReader.

It is interesting to note that this function will stop on closing tags as well. I have an XML document similar to the following:
<root>
 <columns>
  <column>columnX</column>
  <column>columnY</column>
 </columns>
 <table>
  <row>
   <columnX>38</columnX>
   <columnY>50</columnY>
  </row>
  <row>
   <columnX>82</columnY>
   <columnY>28</columnY>
  </row>
  ...
 </table>
</root>
I need to parse the <columns> object to know what attributes to check for from each <row> node. Therefore I was doing the following:
<?php
while ($xml->read()) {
 if ($xml->name === 'column') {
  //parse column node to into $columns array
 }
 elseif ($xml->name === 'row') {
  //parse row node, using constructed $columns array
 }
}
?>
This kind of worked in that I ended up with an array of all the data I wanted, but the array I constructed was twice as large as I expected and every other entry was empty. Took me a while to debug, but finally figured out that checking <?php $xml->name === 'row' ?> matches both <row> and </row>, so the check should really be something more like:
<?php
if ($xml->name === 'row' && $xml->nodeType == XMLReader::ELEMENT) {
 // parse row node
}
?>
I would have liked to use the next() function instead, but as I needed to parse 2 different subtrees, I couldn't figure out how to find all the columns, reset the pointer, and then find all the rows.

Another approach to the 'also reads closing tags' gotcha:
<?php
$reader = new XMLReader();
$reader->open('users.xml');
while ($reader->read()) {
 if ($reader->nodeType == XMLReader::END_ELEMENT) {
  continue; //skips the rest of the code in this iteration
 }
 //do something with desired node type
 if($reader->name == 'user') {
  //...
 }
}
?>

If like myself you have been turning the interwebz upside down looking for a solution for this issue:
PHP Warning: XMLReader::read(): /tmp/xml_feed.xml:4183934: parser error : Input is not proper UTF-8, indicate encoding !
For some reason, this warning breaks the execution - is it a fatal error in disguise?
After days of frustration I found it!!!!
tidy -xml -o output.xml -utf8 -f error.log input.xml
You can invoque tidy using exec, It takes several seconds to convert a 250Mb feed, but it worthy the time.
In my case the issue was with latin1 charset, and for some reason I had to pass the xml through tidy 2 times - first time around creates new errors, second time it fixes everything.
I know invalid xml should be fixed by xml creators, but it works differently in the real world.

> I would have liked to use the next() function instead, but as I needed to parse 2 different subtrees, I couldn't figure out how to find all the columns, reset the pointer, and then find all the rows. 
I just use:
$reader->close();
$reader->open($url);
to reset the pointer.

A very simple way to avoid typing $reader->read() multiple times when you want to skip some nodes:
<?php
class smartXMLReader extends XMLReader {
  public function readTimes($count) {
    $i = 0;
    while($i < $count){
      $this->read();
      $i++;
    }
  }
}
?>
Using this smartXMLReader, 
<?php
$reader->readTimes(3);
?>
is equivalent to 
<?php
$reader->read();
$reader->read();
$reader->read();
?>
Makes getting around in your XML document a bit easier :)