Document fix for 'substr breaks utf-8 strings'

At bottom of this PHP manual page, a chinese user proposes a replacement for substr().

function dbyte_substr($str, $start, $len=''){
       if($len == ''){
               $outstr = substr($str, $start);
       }else{
            $outstr = substr($str, $start, $len);
            // Check the end bound is an double byte first byte or not
            if(preg_match("/[\x80-\xFF]$/", $outstr)){
                   $outstr = substr("$outstr", 0, -1);
            }
     }
       return $outstr;
}

I don't know how valid this solution is.

mb_strcut() is the solution. It is only supported for (php 4 >= 4.0.6). Becuase it is an extended module, it may not be available.

http://www.php.net/manual/function.mb-strcut.php

We may need to backport(or reinvent) this routine.

Bug #2230 is also related.

Instead of substr($str, 0, $length), use this function instead. It may solve the problem.

The proper solution to this problem is to compile PHP with multibyte string support (--enable-mbstring) [see http://www.php.net/manual/en/ref.mbstring.php] and specify mbstring.func_overload in PHP.ini and/or .htaccess to be equal to 7 (overload on all functions).

--enable-mbstring is supposed to be enabled by default on PHP 4.3+, but the comment at the bottom of that page seems to imply that it actually isn't.

Al suggests that the fix for this requires no code change in Drupal. Changing title to reflext that this is a documentation issue.

Fixed by Steven.