自己写的php中文截取函数mb_strlen和mb_substr

众所周知，php 自带的 strlen 与 substr 函数没法处理中文字符，于是，我们会用 mb_ 系列函数替代。但是，没有 mbstring 库怎么办？这就需要我们自己写一个来替代了，废话不多说，先上代码:

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);

    }

}