How to use htmlspecialchars() but keep the <a> tag along with others in PHP?

Question

I am trying to use htmlspecialchars() but want to preserve the following tags:

<a>, <b> and <i>.

How would I go about doing so?

The solutions that I have found do not seem to work together with an attribute tag and a normal plain tag.

Here is a piece of code that I have found that is supposed to allow for tags with attributes:

function fix_attributes($match){
    return "<".$match[1].str_replace('&quot;','"',$match[2]).">";
}
function allow_only($str, $allowed){
    $str = htmlspecialchars($str);
    foreach( $allowed as $a ){
        $str = preg_replace_callback("/&lt;(".$a."){1}([\s\/\.\w=&;:#]*?)&gt;/", fix_attributes, $str);
        $str = str_replace("&lt;/".$a."&gt;", "</".$a.">", $str);
    }
    return $str;
}
echo allow_only('This is <b>bold</b> and <a href="http://www.#links">this</a> is <i>italic</i>.', array("b","a","i"));

Source

However, it keeps giving me an error: Use of undefined constant fix_attributes

I would appreciate any help with this!

Answer 1

Problem: use callback function without quotes

for more info see http://php.net/manual/en/function.preg-replace-callback.php

 <?php
    function fix_attributes($match){
        return "<".$match[1].str_replace('&quot;','"',$match[2]).">";
    }
    function allow_only($str, $allowed){
        $str = htmlspecialchars($str);
        foreach( $allowed as $a ){
            $str = preg_replace_callback("/&lt;(".$a."){1}([\s\/\.\w=&;:#]*?)&gt;/", "fix_attributes", $str);//use quotes here 
            $str = str_replace("&lt;/".$a."&gt;", "</".$a.">", $str);
        }
        return $str;
    }
    echo allow_only('This is <b>bold</b> and <a href="http://www.#links">this</a> is <i>italic</i>.', array("b","a","i"));
    ?>