Not able to get image src using regex - php

Question

I am using below regex to append a element in front of image tag, but it's not working. I took this code from Add link around img tags with regexp
preg_replace('#(<img[^>]+ src="([^"]*)" alt="[^"]*" />)#', '<a href="$2" ...>$1</a>', $str)
However, If I use below code without src, it works.
preg_replace('#(<img[^>]+ alt="[^"]*" />)#', '<a href="" ...>$1</a>', $str)
Any reason why I am not able to get the src from the image tag.
My image tag is <img src="" alt="">

Answer 1

A better way to do something like this is to use PHP's DOMDocument class as it is independent of how people write their HTML (e.g. putting the alt attribute before the src attribute). Something like this would work for your case:
$html = '<div id="x"><img src="/images/xyz" alt="xyz" /><p>hello world!</p></div>';
$doc = new DomDocument();
$doc->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xpath = new DomXPath($doc);
$images = $xpath->query('//img');
foreach ($images as $img) {
// create a new anchor element
$a = $doc->createElement('a');
// copy the img src attribute to the a href attribute
$a->setAttribute('href', $img->attributes->getNamedItem('src')->nodeValue);
// add the a to the images parent
$img->parentNode->replaceChild($a, $img);
// make the image a child of the <a> element
$a->appendChild($img);
}
echo $doc->saveHTML();
Output:
<div id="x"><img src="/images/xyz" alt="xyz"><p>hello world!</p></div>
Demo on 3v4l.org