php - htmlentites not working for emoji

Question

I am trying to show a characters html entity

echo htmlentities(htmlentities("&"));
//outputs &
echo htmlentities(htmlentities("<"));
//outputs &lt;

but it does not seem to work with emoji

echo htmlentities(htmlentities("??"));
//outputs ??

How can I get it to output 😎?

---

Edit:

I am trying to display a string input by the user with all of the html entities encoded.
echo htmlentities(htmlentities($input))

Example: "this & that ??" -> "this & that 😎"

Answer 1

This works for regular HTML entities, UTF-8 emoticons (and other utf stuff) as well as regular strings of course.

I was just having trouble with empty string value, so I had to put this condition into the function.

function entities( $string ) {
    $stringBuilder = "";
    $offset = 0;

    if ( empty( $string ) ) {
        return "";
    }

    while ( $offset >= 0 ) {
        $decValue = ordutf8( $string, $offset );
        $char = unichr($decValue);

        $htmlEntited = htmlentities( $char );
        if( $char != $htmlEntited ){
            $stringBuilder .= $htmlEntited;
        } elseif( $decValue >= 128 ){
            $stringBuilder .= "&#" . $decValue . ";";
        } else {
            $stringBuilder .= $char;
        }
    }

    return $stringBuilder;
}

// source - http://php.net/manual/en/function.ord.php#109812
function ordutf8($string, &$offset) {
    $code = ord(substr($string, $offset,1));
    if ($code >= 128) {        //otherwise 0xxxxxxx
        if ($code < 224) $bytesnumber = 2;                //110xxxxx
        else if ($code < 240) $bytesnumber = 3;        //1110xxxx
        else if ($code < 248) $bytesnumber = 4;    //11110xxx
        $codetemp = $code - 192 - ($bytesnumber > 2 ? 32 : 0) - ($bytesnumber > 3 ? 16 : 0);
        for ($i = 2; $i <= $bytesnumber; $i++) {
            $offset ++;
            $code2 = ord(substr($string, $offset, 1)) - 128;        //10xxxxxx
            $codetemp = $codetemp*64 + $code2;
        }
        $code = $codetemp;
    }
    $offset += 1;
    if ($offset >= strlen($string)) $offset = -1;
    return $code;
}

// source - http://php.net/manual/en/function.chr.php#88611
function unichr($u) {
    return mb_convert_encoding('&#' . intval($u) . ';', 'UTF-8', 'HTML-ENTITIES');
}

/* ---- */

var_dump( entities( "&" ) ) . "
";
var_dump( entities( "<" ) ) . "
";
var_dump( entities( "??" ) ) . "
";
var_dump( entities( "?" ) ) . "
";
var_dump( entities( "" ) ) . "
";
var_dump( entities( "A" ) ) . "
";
var_dump( entities( "Hello ?? world" ) ) . "
";
var_dump( entities( "this & that ??" ) ) . "
";