Problem in updating an XML file using PHP DOMDocument(); - php

Question

I am trying to write a function that updates the Site Map of a website or technically adds an entry to sitemap.xml file. The standard structure of a Google sitemap can be seen here: http://www.sitemappro.com/google-sitemap.html
Following is the code of that function:
function AddEntry($loc,$lastmod,$changefreq,$priority){
$xmlDoc = new DOMDocument();
$xmlDoc->load("sitemap.xml");
$url []=array('loc' => $loc, 'lastmod' => $lastmod, 'changefreq'=> $changefreq, 'priority' =>$priority );
$r=$xmlDoc->createElement("url");
$xmlDoc->appendChild($r);
foreach($url as $key=>$value)
{
$r->appendChild($xmlDoc->createElement($key))->appendChild($xmlDoc->createTextNode($value));
}
$xmlDoc->save();
}
The above code is not working and giving this error:
"Fatal error: Uncaught exception 'DOMException' with message 'Invalid Character Error' in..."
Can you please help by correcting my code? Thanks in advance.

Answer 1

As pointed out in a comment the issue should be in this line
$r->appendChild($xmlDoc->createElement($key))->appendChild($xmlDoc->createTextNode($value));
Most likely you're adding some url characters to your XML. The problem is that you must escape them or surround your $value with a CDATA section. Otherwise the generated XML will be invalid and the xml library will throw that kind of exceptions.
P.S. I don't remember if the htmlentities function is good also for xml, I suppose that, but you'll need to investigate about that.