PHP截取接口

 public function common_substr($str, $start, $length, $encoding){ //截取方法
          /*mb_substr( $str, $start, $length, $encoding )
             $str，需要截断的字符串
             $start，截断开始处，起始处为0
             $length，要截取的字数
             $encoding，网页编码，如utf-8,GB2312,GBK
             */
          return mb_substr( $str, $start, $length, $encoding );
    }