function backup($bakfile = null, $tables = array())
 {
  if (empty($bakfile)) {
   $bakfile = $this->dbname . date(ymdhis) . '.sql';
  } elseif (is_dir($bakfile)) {
   if (preg_match('//$/', $bakfile)) {
    $bakfile = $bakfile . $this->dbname . date(ymdhis) . '.sql';
   } else {
    $bakfile = $bakfile . '/' . $this->dbname . date(ymdhis) . '.sql';
   }
  }
  if (!$tables) {
   $this->query(show tables);
   while ($row = mysql_fetch_row($this->queryid)) {
    $tables[] = $row[0];
   }
  } else {
   foreach ($tables as $k => $v) {
    $tables[$k] = $this->tableprefix . $v;
   }
  }
if ($fp = fopen($bakfile, 'wb')) {
   if ($this->dbcharset) {
    fwrite($fp, set names . $this->dbcharset . ;nn);
   }
   foreach ($tables as $table) {
    $this->dumptable($table, $fp);
    fwrite($fp, n);
   }//foreach
   fclose($fp);
   return true;
  } else {
   return false;
  }//if
 }
//私有方法 导出表格
 function dumptable($fulltablename, $fp)
 {
  //备份表结构 
  fwrite($fp, -- n-- {$fulltablename}n-- n);
  $row = $this->findbysql(show create table `{$fulltablename}`);
  fwrite($fp, $row['create table'] . ;nn );
  //备份表库数据
  $this->query(select * from `{$fulltablename}`);
  while ($row = mysql_fetch_assoc($this->queryid)) {
   foreach ($row as $k=>$v) {
    $row[$k] = ' . $this->qstr($v) . ' ;
   }
   $sql = insert into `$fulltablename` values ( . join(,, $row) . );n;
   fwrite($fp, $sql);
  }
  mysql_free_result($this->queryid);
  fwrite($fp, n);
 }
//恢复数据库文件
 function restore($bakfile)
 {
  if ($fp = fopen($bakfile, 'r')) {
   $sql = '';
   while (!feof($fp)) {
    $line = fgets($fp);
    if (strpos($line,'--')!==0)
    {
     $sql .= $line;
     //pp($sql);
    }
    if (preg_match('/;s*$/', $sql)) {
     $this->query($sql);
     $sql = '';
    }
   }
   fclose($fp);
   return true;
  } else {
   return false;
  }
 }