php 自己写的简单数据库类

<?php  //header('content-type:text/html;charset=utf-8');  class DB{      private $host;  private $port;  private $user;  private $pass;  private $char;  private $db;  public function __construct($arr = array()){  $this ->host = isset($arr['host']) ? $arr['host'] : '127.0.0.1';  $this ->port = isset($arr['port']) ? $arr['port'] : '3306';  $this ->user = isset($arr['user']) ? $arr['user'] : 'root';  $this ->pass = isset($arr['pass']) ? $arr['pass'] : 'root';  $this ->char = isset($arr['char']) ? $arr['char'] : 'utf8';  $this ->db = isset($arr['db']) ? $arr['db'] : 'school';  $this -> conn();  $this -> dbquery("set names {$this->char}");  $this -> dbquery("use {$this->db}");  }  private function conn(){      @mysql_connect($this->host.':'.$this->port,$this->user,$this->pass) or die('数据库连接失败！');  }  public function dbquery($sql){      $res=@mysql_query($sql);      if(!$res){$this->showerr();}  }  public function dbinsert($sql){      $res=@mysql_query($sql);      if(!$res){$this->showerr();}  return mysql_insert_id();  }  public function dbupdate($sql){      $res=@mysql_query($sql);      if(!$res){$this->showerr();}  return mysql_affected_rows();  }  public function dbselect($sql){      $res=@mysql_query($sql);      if(!$res){$this->showerr();}  while($row=mysql_fetch_assoc($res)){  $arr[]=$row;  }  return $arr;  }  private function showerr(){  echo 'SQL请求错误：'.mysql_errno().':'.mysql_error();exit;  }  }  /*  $db=new DB;  var_dump($db);    var_dump($db->dbselect('select * from pr_student'));  var_dump($db->dbinsert("insert into pr_iuser values(null,'xiaodong',{SHA1(789456)})"));  var_dump($db->dbupdate("update pr_iuser set uname = 'xiaoming' where id='9'"));  */?>