Remove non-utf8 characters from string

You can use mbstring:

$text = mb_convert_encoding($text, 'UTF-8', 'UTF-8');

...will remove invalid characters.

See: Replacing invalid UTF-8 characters by question marks, mbstring.substitute_character seems ignored

Using a regex approach:

$regex = <<<'END'
/
  (
    (?: [\x00-\x7F]                 # single-byte sequences   0xxxxxxx
    |   [\xC0-\xDF][\x80-\xBF]      # double-byte sequences   110xxxxx 10xxxxxx
    |   [\xE0-\xEF][\x80-\xBF]{2}   # triple-byte sequences   1110xxxx 10xxxxxx * 2
    |   [\xF0-\xF7][\x80-\xBF]{3}   # quadruple-byte sequence 11110xxx 10xxxxxx * 3 
    ){1,100}                        # ...one or more times
  )
| .                                 # anything else
/x
END;
preg_replace($regex, '$1', $text);

It searches for UTF-8 sequences, and captures those into group 1. It also matches single bytes that could not be identified as part of a UTF-8 sequence, but does not capture those. Replacement is whatever was captured into group 1. This effectively removes all invalid bytes.

It is possible to repair the string, by encoding the invalid bytes as UTF-8 characters. But if the errors are random, this could leave some strange symbols.

$regex = <<<'END'
/
  (
    (?: [\x00-\x7F]               # single-byte sequences   0xxxxxxx
    |   [\xC0-\xDF][\x80-\xBF]    # double-byte sequences   110xxxxx 10xxxxxx
    |   [\xE0-\xEF][\x80-\xBF]{2} # triple-byte sequences   1110xxxx 10xxxxxx * 2
    |   [\xF0-\xF7][\x80-\xBF]{3} # quadruple-byte sequence 11110xxx 10xxxxxx * 3 
    ){1,100}                      # ...one or more times
  )
| ( [\x80-\xBF] )                 # invalid byte in range 10000000 - 10111111
| ( [\xC0-\xFF] )                 # invalid byte in range 11000000 - 11111111
/x
END;
function utf8replacer($captures) {
  if ($captures[1] != "") {
    // Valid byte sequence. Return unmodified.
    return $captures[1];
  }
  elseif ($captures[2] != "") {
    // Invalid byte of the form 10xxxxxx.
    // Encode as 11000010 10xxxxxx.
    return "\xC2".$captures[2];
  }
  else {
    // Invalid byte of the form 11xxxxxx.
    // Encode as 11000011 10xxxxxx.
    return "\xC3".chr(ord($captures[3])-64);
  }
}
preg_replace_callback($regex, "utf8replacer", $text);

EDIT:

• !empty(x) will match non-empty values ("0" is considered empty).
• x != "" will match non-empty values, including "0".
• x !== "" will match anything except "".

x != "" seem the best one to use in this case.

I have also sped up the match a little. Instead of matching each character separately, it matches sequences of valid UTF-8 characters.

If you apply utf8_encode() to an already UTF8 string it will return a garbled UTF8 output.

I made a function that addresses all this issues. It´s called Encoding::toUTF8().

You dont need to know what the encoding of your strings is. It can be Latin1 (ISO8859-1), Windows-1252 or UTF8, or the string can have a mix of them. Encoding::toUTF8() will convert everything to UTF8.

I did it because a service was giving me a feed of data all messed up, mixing those encodings in the same string.

Usage:

require_once('Encoding.php'); 
use \ForceUTF8\Encoding;  // It's namespaced now.

$utf8_string = Encoding::toUTF8($mixed_string);

$latin1_string = Encoding::toLatin1($mixed_string);

I've included another function, Encoding::fixUTF8(), which will fix every UTF8 string that looks garbled product of having been encoded into UTF8 multiple times.

Usage:

require_once('Encoding.php'); 
use \ForceUTF8\Encoding;  // It's namespaced now.

$utf8_string = Encoding::fixUTF8($garbled_utf8_string);

Examples:

echo Encoding::fixUTF8("Fédération Camerounaise de Football");
echo Encoding::fixUTF8("Fédération Camerounaise de Football");
echo Encoding::fixUTF8("FÃÂédÃÂération Camerounaise de Football");
echo Encoding::fixUTF8("Fédération Camerounaise de Football");

will output:

Fédération Camerounaise de Football
Fédération Camerounaise de Football
Fédération Camerounaise de Football
Fédération Camerounaise de Football

Download:

https://github.com/neitanod/forceutf8

This function removes all NON ASCII characters, it's useful but not solving the question:
This is my function that always works, regardless of encoding:

function remove_bs($Str) {  
  $StrArr = str_split($Str); $NewStr = '';
  foreach ($StrArr as $Char) {    
    $CharNo = ord($Char);
    if ($CharNo == 163) { $NewStr .= $Char; continue; } // keep £ 
    if ($CharNo > 31 && $CharNo < 127) {
      $NewStr .= $Char;    
    }
  }  
  return $NewStr;
}

How it works:

echo remove_bs('Hello õhowå åare youÆ?'); // Hello how are you?