How to make substr_replace match the whole string - php

Question

<?php
$titledb = array('经济管理','管理','others');
$content='经济管理是我们国的家的中心领导力，这是中文测度。';
$replace='<a target="_blank" href="http://www.a.com/$1">$1</a>';
foreach ($titledb as $title) {
$regex = "~\b(" . preg_quote($title) . ")\b~u";
$content = preg_replace($regex, $replace, $content, 1);
}
echo $content;
?>
I was writing a auto link function for my wordpress site and I'm using substr_replace to find the keywords(which are litterally a lot) and replace it with link--I'm doing this by filtering the post content of course.
But in some circumstances, suppose there are posts with titles like "stackoverflow" and "overflow" it turns out to be a mess, the output will look like :
we love<a target="_blank" href="http://www.a.com/stackoverflow">stackoverflow</a>，this is a test。we love <a target="_blank" href="http://www.a.com/stack<a target=" _blank"="">overflow</a> ">stackoverflow，this is a test。
What I want is:
we love<a target="_blank" href="http://www.a.com/stackoverflow">stackoverflow</a>，this is a test。we love stack<a target="_blank" href="http://www.a.com/overflow">overflow</a>，this is a test。
And this is only a test.The production enviorment could be more complicated,like I said there are tens of thousands of titles as keywords need to be found and replaced with a link. So I see these broken links a lot.It happens when a title contains another title.Like title 'stackoverflow' contains another title 'overflow'.
So my question is how to make substr_replace take title 'stackoverflow' as a whole and replace only once? Of course,'overflow' still needs to be replaced somewhere else just not when it is included in another keyword.
Thank you in advance.

Answer 1

To prevent that a search for a word will start replacing inside the HTML code that you already injected for some other word, you could make use of a temporary placeholder, and do the final replacement on those place holders:
$titledb = array('经济管理','管理','others');
// sort the array from longer strings to smaller strings, to ensure that
// a replacement of a longer string gets precedence:
usort($titledb, function ($a,$b){ return strlen($b)-strlen($a); });
$content='经济管理是我们国的家的中心领导力。';
foreach ($titledb as $index => $title) {
$pos = strpos($content, $title);
if ($pos !== false) {
// temporarily insert a place holder in the format '#number#':
$content = substr_replace($content, "#$index#", $pos, strlen($title));
}
}
// Now replace the place holders with the final hyperlink HTML code
$content = preg_replace_callback("~#(\d+)#~u", function ($match) use ($titledb) {
return "<a target='_blank' href='http://www.a.com/{$titledb[$match[1]]}'>{$titledb[$match[1]]}</a>";
}, $content);
echo $content;
See it run on eval.in