//无乱码截取字符串，中英文混合    function left($str, $len, $charset="utf-8"){        //如果截取长度小于等于0，则返回空        if( !is_numeric($len) or $len <= 0 ){            return "";        }        //如果截取长度大于总字符串长度，则直接返回当前字符串        $sLen = strlen($str);        if( $len >= $sLen ){            return $str;        }         if ( strtolower($charset) == "utf-8" ){            $len_step = 3;         }else{            $len_step = 2;         }         $len_i = 0;         $substr_len = 0;        for( $i=0; $i < $sLen; $i++ ){            if ( $len_i >= $len ) break;             if( ord(substr($str,$i,1)) > 0xa0 ){                $i += $len_step - 1;                $substr_len += $len_step;            }else{                 $substr_len ++;            }            $len_i ++;        }        $result_str = substr($str,0,$substr_len );        return $result_str;    }