自己写的php中文截取函数mb_strlen和mb_substr

if ( !function_exists('mb_strlen') ) {
 function mb_strlen ($text, $encode) {
  if ($encode=='UTF-8') {
   return preg_match_all('%(?:
       [/x09/x0A/x0D/x20-/x7E]           # ASCII
     | [/xC2-/xDF][/x80-/xBF]            # non-overlong 2-byte
     |  /xE0[/xA0-/xBF][/x80-/xBF]       # excluding overlongs
     | [/xE1-/xEC/xEE/xEF][/x80-/xBF]{2} # straight 3-byte
     |  /xED[/x80-/x9F][/x80-/xBF]       # excluding surrogates
     |  /xF0[/x90-/xBF][/x80-/xBF]{2}    # planes 1-3
     | [/xF1-/xF3][/x80-/xBF]{3}         # planes 4-15
     |  /xF4[/x80-/x8F][/x80-/xBF]{2}    # plane 16
     )%xs',$text,$out);
  }else{
   return strlen($text);
  }
 }
}

 

/* from Internet, author unknown */
if (!function_exists('mb_substr')) {
    function mb_substr($str, $start, $len = '', $encoding="UTF-8"){
        $limit = strlen($str);
 
        for ($s = 0; $start > 0;--$start) {// found the real start
            if ($s >= $limit)
                break;
 
            if ($str[$s] <= "/x7F")
                ++$s;
            else {
                ++$s; // skip length
 
                while ($str[$s] >= "/x80" && $str[$s] <= "/xBF")
                    ++$s;
            }
        }
 
        if ($len == '')
            return substr($str, $s);
        else
            for ($e = $s; $len > 0; --$len) {//found the real end
                if ($e >= $limit)
                    break;
 
                if ($str[$e] <= "/x7F")
                    ++$e;
                else {
                    ++$e;//skip length
 
                    while ($str[$e] >= "/x80" && $str[$e] <= "/xBF" && $e < $limit)
                        ++$e;
                }
            }
 
        return substr($str, $s, $e - $s);
    }
}