Special Character in XML using PHP

Question

I am trying to generate a XML file with some of the values that contains special characters such as μmol/l, x103 cells/μl and many more. also need functionality to put in superscripts.

I encoded the text μmol/l to something like this using a ordutf8 function from php.net

&#956&#109&#111&#108&#47&#108

function ords_to_unistr($ords, $encoding = 'UTF-8'){
 // Turns an array of ordinal values into a string of unicode characters
 $str = '';
 for($i = 0; $i < sizeof($ords); $i++){
 // Pack this number into a 4-byte string
 // (Or multiple one-byte strings, depending on context.) 
 $v = $ords[$i];
 $str .= pack("N",$v);
 }
 $str = mb_convert_encoding($str,$encoding,"UCS-4BE");
 return($str); 
}
function unistr_to_ords($str, $encoding = 'UTF-8'){ 
 // Turns a string of unicode characters into an array of ordinal values,
 // Even if some of those characters are multibyte.
 $str = mb_convert_encoding($str,"UCS-4BE",$encoding);
 $ords = array();
 // Visit each unicode character
 for($i = 0; $i < mb_strlen($str,"UCS-4BE"); $i++){ 
 // Now we have 4 bytes. Find their total
 // numeric value.
 $s2 = mb_substr($str,$i,1,"UCS-4BE"); 
 $val = unpack("N",$s2); 
 $ords[] = $val[1]; 
 } 
 return($ords);
}

I have sucessfully converted this code back to "richtext" using PHPExcel to generate Excel documents and PDF, but I now need to put it into a XML.

If i use the &# characters as is I get a error message saying

SimpleXMLElement::addChild(): invalid decimal character value

Here are more values I have in the database that needs to be made "XML" friendly

&#120&#49&#48&#60&#115&#117&#112&#62&#54&#60&#47&#115&#117&#112&#62&#32&#99&#101&#108&#108&#115&#47&#181&#108

Converted from x10³ cells/μl

Answer 1

Here is no need to encode these characters. XML strings can use UTF-8 or another encoding. Depending on the encoding the serializer will encode as necessary.

$foo = new SimpleXmlElement('<?xml version="1.0" encoding="UTF-8"?><foo/>');
$foo->addChild('bar', 'μmol/l, x103 cells/μl'); 
echo $foo->asXml();

Output (special characters not encoded):

<?xml version="1.0" encoding="UTF-8"?>
<foo><bar>μmol/l, x103 cells/μl</bar></foo>

To force entities for the special characters, you need to change the encoding:

$foo = new SimpleXmlElement('<?xml version="1.0" encoding="ASCII"?><foo/>');
$foo->addChild('bar', 'μmol/l, x103 cells/μl');
echo $foo->asXml();

Output (special characters encoded):

<?xml version="1.0" encoding="ASCII"?>
<foo><bar>&#956;mol/l, x10&#179; cells/&#181;l</bar></foo>

I suggest you convert your custom encoding back to UTF-8. That way the XML Api can take care of it. If you like to store string with the custom encoding you need to work around a bug.

A string like &#120&#49&#48&#60&#115&#117 triggers a bug in SimpleXML/DOM. The second argument of SimpleXMLElement::addChild() and DOMDocument::createElement() have a broken escaping. You need to create the content as text node and append it.

Here is a small class that extends SimpleXMLElement and adds a workaround:

class MySimpleXMLElement extends SimpleXMLElement {
 public function addChild($nodeName, $content = NULL) {
 $child = parent::addChild($nodeName);
 if (isset($content)) {
 $node = dom_import_simplexml($child);
 $node->appendChild($node->ownerDocument->createTextNode($content));
 }
 return $child;
 }
}
$foo = new MySimpleXmlElement('<?xml version="1.0" encoding="UTF-8"?><foo/>');
$foo->addChild('bar', '&#120&#49&#48&#60&#115&#117'); 
echo $foo->asXml();

Output:

<?xml version="1.0" encoding="UTF-8"?>
<foo><bar>&amp;#120&amp;#49&amp;#48&amp;#60&amp;#115&amp;#117</bar></foo>

The & from your custom encoding get escaped as the entity & - because it is an special character in XML. The XML parser will decode it.

$xml = <<<'XML'
<?xml version="1.0" encoding="UTF-8"?>
<foo><bar>&amp;#120&amp;#49&amp;#48&amp;#60&amp;#115&amp;#117</bar></foo>
XML;
$foo = new SimpleXMLElement($xml);
var_dump((string)$foo->bar);

Output:

string(27) "&#120&#49&#48&#60&#115&#117"

• Willem Pretorius: I have these values in the database... &#120&#49&#48&#60&#115&#117&#112&#62&#54&#60&#47&#115&#117&#112&#62&#32&#99&#101&#108&#108&#115&#47&#181&#108