Get multiple headings and the first paragraph for each heading

Question

I have a hard time figuring out how I can get multiple headings and the first paragraph for that heading. In this case I only need the h3 titles and the following paragraph for each.

Example code

function everything_in_tags($string, $tagname)
{
    $pattern = "#<\s*?$tagname\b[^>]*>(.*?)</$tagname\b[^>]*>#s";
    preg_match($pattern, $string, $matches);
    return $matches[1];
}
$tagname = "h3";

$string = "<h1>This is my title</h1>

<p>This is a text right under my h1 title.</p>
<p>This is some more text under my h1 title</p>

<h2>This is my level 2 heading</h2>
<p>This is text right under my level 2 heading</p>

<h3>First h3</h3>
<p>First paragraph for the first h3</p>

<h3>Second h3</h3>
<p>First paragraph for the second h3</p>

<h3>Third h3</h3>
<p>First paragraph for the third h3</p>
<p>Second paragraph for the third h3</p>

<h2>This is my level 2 heading</h2>
<p>This is text right under my level 2 heading</p>";

//OUTPUT: First h3
echo everything_in_tags($string, $tagname);

I would like to implement a foreach loop - but that requires that the above is working as expected.

foreach ($headings as $heading && $paragraphs as $paragraph) {
    echo "<h3>".$heading."</h3>";
    echo "<p>".$paragraph."</p>";
}

//Expected output:
//<h3>First h3</h3>
//<p>First paragraph for the first h3</p>

//<h3>Second h3</h3>
//<p>First paragraph for the second h3</p>

//<h3>Third h3</h3>
//<p>First paragraph for the third h3</p>

So in above example I can get the first h3. But after a lot of reading, I can't seem to find out how to get all the h3's and the first paragraphs for each as well.

If anyone can point me in the right direction and explain to me how to do this I would really appreciate it. Thank you.

Answer 1

There is an obligatory defacto answer to this, and it is to not use RegEx for HTML. There are exceptions for controlled HTML, or where mistakes/bugs don't really matter, but generally, I would agree with that, and instead I'd point you at a DOM-aware thing where you could express things like HTML tags and the concept of "next".

Here's a sample that works, although you'll probably need to tweak where I'm dumping.

<?php

$html = <<<TAG
<h1>This is my title</h1>

<p>This is a text right under my h1 title.</p>
<p>This is some more text under my h1 title</p>

<h2>This is my level 2 heading</h2>
<p>This is text right under my level 2 heading</p>

<h3>First h3</h3>
<p>First paragraph for the first h3</p>

<h3>Second h3</h3>
<p>First paragraph for the second h3</p>

<h3>Third h3</h3>
<p>First paragraph for the third h3</p>
<p>Second paragraph for the third h3</p>

<h2>This is my level 2 heading</h2>
<p>This is text right under my level 2 heading</p>
TAG;


$dom = new DomDocument();
// Load the HTML, don't worry about it being a fragment
$dom->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);

$xpath = new DOMXPath($dom);

// Grab all H3 tags. This might need to be adjusted if there's more to the depth
$results = $xpath->query("//h3");
foreach ($results as $result) {
    var_dump(sprintf('<h3>%1$s</h3>', $result->textContent));
    
    // See if the next element is a P tag
    $next = $result->nextElementSibling;
    if ($next && 'p' === $next->nodeName) {
        var_dump(sprintf('<p>%1$s</p>', $next->textContent));
    }
}

Output:

string(17) "<h3>First h3</h3>"
string(39) "<p>First paragraph for the first h3</p>"
string(18) "<h3>Second h3</h3>"
string(40) "<p>First paragraph for the second h3</p>"
string(17) "<h3>Third h3</h3>"
string(39) "<p>First paragraph for the third h3</p>"

Demo here: https://3v4l.org/gvBrv