Make strip_tags replace HTML with entities instead of nothing

Question

I have this line of code:

$content = strip_tags($content, '<a><br><b><i>');

It works like it should, but I need for users to be able to enter code and for the code to be displayed on the web-page.
For example,

<?php
echo 'Hey';
?>

displays nothing. I need it to display

<?php
echo 'Hey';
?>

for example. What function should I use to do this?
EDIT: To clarify, the user sees the PHP code, it just gets replaced with HTML entities so the server doesn't try to run it.

Answer 1

Try:

$content = htmlspecialchars(strip_tags($content, '<a><br><b><i>'));

Or

$content = htmlentities(strip_tags($content, '<a><br><b><i>'), ENT_QUOTES);

See htmlspecialchars and htmlentities .