Question

I am trying to replace a tag from a xml. I have stored a xml results through curl in variable. and trying to make a file.xml.
when it

  <Topics>
  <Topic code="Balances" count="26" pagesize="100" />
  </Topics>

with this function , it doesnt return any matches. why?

 function get_tag( $tag, $xml ) {
    $tag = preg_quote($tag);

     preg_match_all('{<'.$tag.'[^>]*>(.*?)</'.$tag.'>}',
               $xml,
               $matches,
               PREG_PATTERN_ORDER);

  return $matches[1];
 }

Answer 1

Your example is a very poor and slow implementation of parsing a document. Suggestively you should have a look at the DOMDocument object and try to implement it.

Basic usage according to your example:

$dom = new DOMDocument();
$dom->loadXML("<xml ... />"); // Current document

$replace = $dom->getElementsByTagName($tag);

foreach ($replace as $node)
{
    $xml = $dom->createDocumentFragment();
    $xml->loadXML("<xml ... />"); // XML to replace original with

    $dom->replaceChild($xml, $node); // XML is your new node
}

$dom->normalize(); // Saves the changes
echo $dom->saveXML(); // Output

Edit; Sorry – better example now.