PHP截取中文字符串方法详解

php自带的一个截取字符串的函数substr，但其只能处理英文、数字却不能截取中文混排的。如果需要在PHP中进行GB2312与UTF-8的互换，需要php_iconv.dll的支持（PHP4中包含此文件）。php5内建支持iconv，更加方便了。不管是uft-8编码转换为gb2312,还是将 gb2312 转换为 uft-8，PHP4.3.1以后的iconv函数很方便，只是需要自己写一个uft8到unicode的转换函数。处理中文的字符串截取函数mb_substr()是在PHP4.0.6后引入的，其自身支持不同编码字符的处理，所以一些新的PHP框架其实已经支持mb_substr()了。

处理函数汇总：

 function cutstr($string, $length, $dot = ' ...')
 {   //截字符串函数    GBK,UTF8
     $charset = 'utf-8';

     if(strlen($string) <= $length)
     {   //边界条件
         return $string;
     }

     $string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);

     $strcut = '';
     if(strtolower($charset) == 'utf-8') {

         $n = $tn = $noc = 0;
         while($n < strlen($string)) {

         $t = ord($string[$n]);
         if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
             $tn = 1; $n++; $noc++;
         } elseif(194 <= $t && $t <= 223) {
             $tn = 2; $n += 2; $noc += 2;
         } elseif(224 <= $t && $t <= 239) {
             $tn = 3; $n += 3; $noc += 2;
         } elseif(240 <= $t && $t <= 247) {
             $tn = 4; $n += 4; $noc += 2;
         } elseif(248 <= $t && $t <= 251) {
             $tn = 5; $n += 5; $noc += 2;
         } elseif($t == 252 || $t == 253) {
             $tn = 6; $n += 6; $noc += 2;
         } else {
             $n++;
         }

         if($noc >= $length) {
             break;
         }

     }
     if($noc > $length)
     {
         $n -= $tn;
     }

     $strcut = substr($string, 0, $n);

     } else
     {
         for($i = 0; $i < $length; $i++)
         {
             $strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
         }
     }

     $strcut = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $strcut);

     return $strcut.$dot;
 }

方法二：

 function len($string, $sublen = 80, $etc = '...',$break_words = false, $middle = false)
 {
 $start=0;
 $code="UTF-8";
        if($code == 'UTF-8')
    {
        $pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
        preg_match_all($pa, $string, $t_string);
        if(count($t_string[0]) - $start > $sublen) return join('', array_slice($t_string[0], $start, $sublen))."...";
        return join('', array_slice($t_string[0], $start, $sublen));
    }
    else
    {
        $start = $start*2;
        $sublen = $sublen*2;
        $strlen = strlen($string);
        $tmpstr = '';
        for($i=0; $i<$strlen; $i++)
        {
            if($i>=$start && $i<($start+$sublen))
            {
                if(ord(substr($string, $i, 1))>129)
                {
                    $tmpstr.= substr($string, $i, 2);
                }
                else
                {
                    $tmpstr.= substr($string, $i, 1);
                }
            }
            if(ord(substr($string, $i, 1))>129) $i++;
        }
        if(strlen($tmpstr)<$strlen ) $tmpstr.= "...";
        return $tmpstr;
    }
 }

方法三（兼容mb_substr）：

 /**
  +----------------------------------------------------------
  * 字符串截取，支持中文和其他编码
  +----------------------------------------------------------
  * @static
  * @access public
  +----------------------------------------------------------
  * @param string $str 需要转换的字符串
  * @param string $start 开始位置
  * @param string $length 截取长度
  * @param string $charset 编码格式
  * @param string $suffix 截断显示字符
  +----------------------------------------------------------
  * @return string
  +----------------------------------------------------------
  */
 function msubstr($str, $start, $length, $charset="utf-8", $suffix=true)
 {
     if(function_exists("mb_substr")){
         $slice = mb_substr($str, $start, $length, $charset);
     }elseif(function_exists('iconv_substr')) {
         $slice = iconv_substr($str,$start,$length,$charset);
         if(false === $slice) {
             $slice = '';
         }
     }else{
         $re['utf-8']   = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/";
         $re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/";
         $re['gbk']    = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/";
         $re['big5']   = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/";
         preg_match_all($re[$charset], $str, $match);
         $slice = join("",array_slice($match[0], $start, $length));
     }
     return $suffix ? $slice.'...' : $slice;
 }