PHP - Fast way to strip all characters not displayable in browser from utf8 string

Question

I\'ve got a little messy database containing names of many institutions around the world.

I want to display them including national characters, but without invalid c

Answer 1

If the database is the issue which it seems to be in your case (and fixing it is out of the way) then maybe just print out each character from the string using ORD and find the value for the control character that is not well sent.

Then when you know the control character value, pass these values into a function that searches for that control character and try to change the utf-8 encoding (the flawed one) with corresponding UTF8 characters live.

Answer 2

I want to just filter it out

You have got an unspecified encoding/charset with your data. This is a huge problem.

You can first try to convert it into utf-8 and then strip all non-printable characters:

$str = iconv('utf-8', 'utf-8//ignore', $str);

echo preg_replace('/[^\pL\pN\pP\pS\pZ]/u', '', $str);

The problem is, that the iconv function can only try. It will drop any invalid character sequence. As of php 5.4 it will drop the complete string however, if the input encoding specified is invalid.

You will see a warning since PHP 5.3 already that the input string has an invalid encoding.

You can go around this by removing all invalid utf-8 byte sequences first:

$str = valid_utf8_bytes($str);

echo preg_replace('/[^\pL\pN\pP\pS\pZ]/u', '', $str);

/**
 * get valid utf-8 byte squences
 *
 * take over all matching bytes, drop an invalid sequence until first
 * non-matching byte.
 * 
 * @param string $str
 * @return string
 */
function valid_utf8_bytes($str)
{
    $return = '';
    $length = strlen($str);
    $invalid = array_flip(array("\xEF\xBF\xBF" /* U-FFFF */, "\xEF\xBF\xBE" /* U-FFFE */));

    for ($i=0; $i < $length; $i++)
    {
        $c = ord($str[$o=$i]);

        if ($c < 0x80) $n=0; # 0bbbbbbb
        elseif (($c & 0xE0) === 0xC0) $n=1; # 110bbbbb
        elseif (($c & 0xF0) === 0xE0) $n=2; # 1110bbbb
        elseif (($c & 0xF8) === 0xF0) $n=3; # 11110bbb
        elseif (($c & 0xFC) === 0xF8) $n=4; # 111110bb
        else continue; # Does not match

        for ($j=++$n; --$j;) # n bytes matching 10bbbbbb follow ?
            if ((++$i === $length) || ((ord($str[$i]) & 0xC0) != 0x80))
                continue 2
        ;

        $match = substr($str, $o, $n);

        if ($n === 3 && isset($invalid[$match])) # test invalid sequences
            continue;

        $return .= $match;
    }
    return $return;
}

Answer 3

The database might not be the problem entirely - if the tables are utf8 encoded the strings in them should have been converted (I think). The issue I've ran into with this has been a matter of correctly ensuring the encoding is consistent. For instance the mysqli connector, by default, reverts to Latin-8859 IIRC so it's quite possible to have the output in utf8, the database in utf8 and still end up with ? characters because they're converted to Latin by the mysqli connector.

To ensure utf8 across the board you need to do something like:

In the database:

ensure the collation is something like utf8_general_ci

At the top of the PHP view file:

<?php header('Content-Type:Text/Plain;charset=utf-8'); ?>

In the HTML meta tag (optional):

<meta http-equiv="content-type" content="text/html;charset=utf-8" />

AND in the database connector (using MySQLi as an example):

mysqli::set_charset('utf8'); #note that for MySQL it isn't hyphenated

You might find that resolves the problem anyway.