Decoding numeric html entities via PHP

I have this code to decode numeric html entities to the UTF8 equivalent character.

I'm trying to convert this character:

’

which should output:

?

However, it just disappears (no output). (i've checked the source code of the page, the page has the correct utf8 character set headers/meta tags).

Does anyone know what is wrong with the code?

function entity_decode($string, $quote_style = ENT_COMPAT, $charset = "UTF-8") {    
     $string = html_entity_decode($string, $quote_style, $charset);

     $string = preg_replace_callback('~&#x([0-9a-fA-F]+);~i', "chr_utf8_callback", $string);
     $string = preg_replace('~&#([0-9]+);~e', 'chr_utf8("\1")', $string);

    //this is another method, which also doesn't work.. 
     //$string = preg_replace_callback("/(&#[0-9]+;)/", "entity_decode_callback", $string);

     return $string; 
}




function chr_utf8_callback($matches) { 
     return chr_utf8(hexdec($matches[1])); 
}

function chr_utf8($num) {   
     if ($num < 128) return chr($num);
     if ($num < 2048) return chr(($num >> 6) + 192) . chr(($num & 63) + 128);
     if ($num < 65536) return chr(($num >> 12) + 224) . chr((($num >> 6) & 63) + 128) . chr(($num & 63) + 128);
     if ($num < 2097152) return chr(($num >> 18) + 240) . chr((($num >> 12) & 63) + 128) . chr((($num >> 6) & 63) + 128) . chr(($num & 63) + 128);
     return '';
}

function entity_decode_callback($m) { 
     return mb_convert_encoding($m[1], "UTF-8", "HTML-ENTITIES"); 
} 

 echo '=' . entity_decode('&#146;');