Remove unwanted characters from all elements in an array

I have this function that strips illegal characters and it works fine.

This is the code.

<?php

function fix_output($value, $key){
    $new_array = array();
    $newstr = '';
    $good[] = 9;  #tab
    $good[] = 10; #nl
    $good[] = 13; #cr
    for($a=32;$a<127;$a++){
        $good[] = $a;
    }
    $len = strlen($value);
    for($b=0;$b < $len; $b++){
        if(in_array(ord($value[$b]), $good)){
            $newstr .= $value[$b];
        }//fi
    }//rof
    $new_array[$key] = $newstr;
    return $new_array;
}

$array = array();
$array['references1'] = 'Foo1 ◻◻◻◻◻◻◻◻◻◻◻◻';
$array['references2'] = 'Foo2 ◻◻◻◻◻◻◻◻◻◻◻◻';

array_walk($array,"fix_output");

print_r($array);

I want to use the PHP function array_walk but when I use print_r($array) it didn't strip the illegal characters. What seems to be the problem with this? Any idea would be of help! Please point out the things that are unclear!

array_walk has the option to let you pass the value by reference. This is what you want to do. See the & in-front of $value:

<?php

function fix_output(&$value, $key) {
    $good = array_merge(range(32, 127), [
        9,   // tab
        10,  // nl
        13   // cr
    ]);
    $value = join("", array_map(
        "chr", 
        array_intersect(
            array_map("ord", str_split($value)), 
            $good
        )
    ));
}

$array = array();
$array['references1'] = 'Foo1 ◻◻◻◻◻◻◻◻◻◻◻◻';
$array['references2'] = 'Foo2 ◻◻◻◻◻◻◻◻◻◻◻◻';

array_walk($array,"fix_output");

print_r($array);

Now your output is:

Array
(
    [references1] => Foo1 
    [references2] => Foo2 
)

I changed the implementation to use more of the array_* functions so you can see how powerful it can be if you combine them. Also not how you can use range() to build the initial good array (also check array_fill_keys).