UTF-8 characters in preg_match_all (PHP)

Question

I have preg_match_all(\'/[aäeëioöuáéíóú]/u\', $in, $out, PREG_OFFSET_CAPTURE);

If $in = \'hëllo\' $out is:

arr         


        

Answer 1

This is not a bug, PREG_OFFSET_CAPTURE refers to the byte offset of the character in the string.

mb_ereg_search_pos behaves the same way. One possibility is to change the encoding to UTF-32 before and then divide the position by 4 (because all unicode code units are represented as 4-byte sequences in UTF-32):

mb_regex_encoding("UTF-32");
$string = mb_convert_encoding('hëllo', "UTF-32", "UTF-8");
$regex =  mb_convert_encoding('[aäeëioöuáéíóú]', "UTF-32", "UTF-8");
mb_ereg_search_init ($string, $regex);
$positions = array();
while ($r = mb_ereg_search_pos()) {
    $positions[] = reset($r)/4;
}
print_r($positions);

gives:

Array
(
    [0] => 1
    [1] => 4
)

You could also convert the binary positions into code unit positions. For UTF-8, a suboptimal implementation is:

function utf8_byte_offset_to_unit($string, $boff) {
    $result = 0;
    for ($i = 0; $i < $boff; ) {
        $result++;
        $byte = $string[$i];
        $base2 = str_pad(
            base_convert((string) ord($byte), 10, 2), 8, "0", STR_PAD_LEFT);
        $p = strpos($base2, "0");
        if ($p == 0) { $i++; }
        elseif ($p <= 4) { $i += $p; }
        else  { return FALSE; }
    }
    return $result;
}

Answer 2

Another way how to split UTF-8 $string by a regular expression is to use function preg_split(). Here is my working solution:

    $result = preg_split('~\[img/\d{1,}/img\]\s?~', $string, -1, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);

PHP 5.3.17

Answer 3

PHP doesn't support unicode very well, so a lot of string functions, including preg_*, still count bytes instead of characters.

I tried finding a solution by encoding and decoding strings, but ultimately it all came down to the preg_match_all function.

About the python thing: a python regex matchobject contains the match position by default mo.start() and mo.end(). See: http://docs.python.org/library/re.html#finding-all-adverbs-and-their-positions

Answer 4

There is simple workaround, to be used after preg_match() results matched. You need to iterate every match result and reassign position value with following:

$utfPosition = mb_strlen(substr($wholeSubjectString, 0, $capturedEntryPosition), 'utf-8');

Tested on php 5.4 under Windows, depends on Multibyte PHP extension only.