PHP实现基本的数据库连接、执行SQL语句及错误提示

<?php
 class database
 {
  private $hostname;
  private $user;
  private $pass;
  private $dbname;
  private $linkflag;
  private $charset;
  function __construct()
  {
   $this->hostname="localhost";
   $this->user="root";
   $this->pass="111";
   $this->dbname="";
   $this->charset="utf8"; //gb2312 GBK utf8
   $this->linkflag=mysql_connect($this->hostname,$this->user,$this->pass);
   mysql_select_db($this->dbname,$this->linkflag) or die($this->error());
   mysql_query("set names ".$this->charset);
  }
  function __set($property_name,$value)
  {
   return $this->$property_name=$value;
  }
  function __get($property_name)
  {
   if(isset($this->$property_name))
   {
    return $this->$property_name;
   }
   else return null;
  }
  function __call($function_name, $args)
  {
    echo "<br><font color=#ff0000>你所调用的方法 $function_name 不存在</font><br>\n";
  }
  function query($sql)
  {
   $res=mysql_query($sql) or die($this->error());
   return $res;
  }
  function fetch_array($res)
  {
   return mysql_fetch_array($res);
  }
  function fetch_object($res)
  {
   return mysql_fetch_object($res);
  }
  function fetch_obj_arr($sql)
  {
   $obj_arr=array();
   $res=$this->query($sql);
   while($row=mysql_fetch_object($res))
   {
    $obj_arr[]=$row;
   }
   return $obj_arr;
  }
  function error()
  {
   if($this->linkflag)
   {
    return mysql_error($this->linkflag);
   }
   else return mysql_error();
  }
  function errno()
  {
   if($this->linkflag)
   {
    return mysql_errno($this->linkflag);
   }
   else return mysql_errno();
  }
  function affected_rows()
  {
   return mysql_affected_rows($this->linkflag);
  }
  function num_rows($sql)
  {
   $res=$this->execute($sql);
   return mysql_num_rows($res);
  }
  function num_fields($res)
  {
   return mysql_num_fields($res);
  }
  function insert_id()
  {
   $previous_id=mysql_insert_id($this->linkflag);
   return $previous_id;
  }
  function result($res,$row,$field=null)
  {
   if($field===null)
   {
    $res=mysql_result($res,$row);
   }
   else $res=mysql_result($res,$row,$field);
   return $res;
  }
  function version()
  {
   return mysql_get_server_info($this->linkflag);
  }
  function data_seek($res,$rowNum)
  {
   return mysql_data_seek($res,$rowNum);
  }
  function __destruct()
  {
   //mysql_close($this->linkflag);
  }
 }
?>