unicode - preg_match and UTF-8 in PHP

Although the u modifier makes both the pattern and subject be interpreted as UTF-8, the captured offsets are still counted in bytes.

You can use mb_strlen to get the length in UTF-8 characters rather than bytes:

$str = "\xC2\xA1Hola!"; preg_match('/H/u', $str, $a_matches, PREG_OFFSET_CAPTURE); echo mb_strlen(substr($str, 0, $a_matches[0][1])); 

Try adding this (*UTF8) before the regex:

preg_match('(*UTF8)/H/u', "\xC2\xA1Hola!", $a_matches, PREG_OFFSET_CAPTURE); 

Magic, thanks to a comment in https://www.php.net/manual/function.preg-match.php#95828

Looks like this is a "feature", see http://bugs.php.net/bug.php?id=37391

'u' switch only makes sense for pcre, PHP itself is unaware of it.

From PHP's point of view, strings are byte sequences and returning byte offset seems logical (i don't say "correct").

Excuse me for necroposting, but may be somebody will find it useful: code below can work both as replacement for preg_match and preg_match_all functions and returns correct matches with correct offset for UTF8-encoded strings.

     mb_internal_encoding('UTF-8');       /**      * Returns array of matches in same format as preg_match or preg_match_all      * @param bool   $matchAll If true, execute preg_match_all, otherwise preg_match      * @param string $pattern  The pattern to search for, as a string.      * @param string $subject  The input string.      * @param int    $offset   The place from which to start the search (in bytes).      * @return array      */     function pregMatchCapture($matchAll, $pattern, $subject, $offset = 0)     {         $matchInfo = array();         $method    = 'preg_match';         $flag      = PREG_OFFSET_CAPTURE;         if ($matchAll) {             $method .= '_all';         }         $n = $method($pattern, $subject, $matchInfo, $flag, $offset);         $result = array();         if ($n !== 0 && !empty($matchInfo)) {             if (!$matchAll) {                 $matchInfo = array($matchInfo);             }             foreach ($matchInfo as $matches) {                 $positions = array();                 foreach ($matches as $match) {                     $matchedText   = $match[0];                     $matchedLength = $match[1];                     $positions[]   = array(                         $matchedText,                         mb_strlen(mb_strcut($subject, 0, $matchedLength))                     );                 }                 $result[] = $positions;             }             if (!$matchAll) {                 $result = $result[0];             }         }         return $result;     }      $s1 = 'Попробуем русскую строку для теста';     $s2 = 'Try english string for test';      var_dump(pregMatchCapture(true, '/обу/', $s1));     var_dump(pregMatchCapture(false, '/обу/', $s1));      var_dump(pregMatchCapture(true, '/lish/', $s2));     var_dump(pregMatchCapture(false, '/lish/', $s2)); 

Output of my example:

    array(1) {       [0]=>       array(1) {         [0]=>         array(2) {           [0]=>           string(6) "обу"           [1]=>           int(4)         }       }     }     array(1) {       [0]=>       array(2) {         [0]=>         string(6) "обу"         [1]=>         int(4)       }     }     array(1) {       [0]=>       array(1) {         [0]=>         array(2) {           [0]=>           string(4) "lish"           [1]=>           int(7)         }       }     }     array(1) {       [0]=>       array(2) {         [0]=>         string(4) "lish"         [1]=>         int(7)       }     } 

You can calculate the real UTF-8 offset by cutting the string to the offset returned by the preg_mach with the byte-counting substr and then measuring this prefix with the correct-counting mb_strlen.

$utf8Offset = mb_strlen(substr($text, 0, $offsetFromPregMatch), 'UTF-8');