<?php

 //$db = new mysqli('localhost:3306','root','','per_position');

 echo '<meta charset="utf-8">';

 class DBDA{

     //定义数据库链接参数

     public $host = 'localhost';

     public $user = 'root';

     public $pwd = '';

     public $database = 'per_position';

     public $charset = 'utf8';

     //数据库连接对象

     public $db = null;

     //DBDA对象

     private static $link = null;

     //禁止构造：初始化数据

     private function __construct($configArr=array()){

         $this->host = isset($configArr['host']) ? $configArr['host'] : 'localhost';

         $this->user = isset($configArr['user']) ? $configArr['user'] : 'root';

         $this->pwd = isset($configArr['pwd']) ? $configArr['pwd'] : '';

         $this->database = isset($configArr['database']) ? $configArr['database'] : 'per_position';

         $this->charset = isset($configArr['charset']) ? $configArr['charset'] : 'utf8';

         //链接数据库

         $this->connect();

     }

     //禁止克隆

     private function __clone(){}

     //提供公有方法返回对象

     static function getDb($config=array()){

         if(!isset(self::$link)){

             self::$link = new self($config);

         }

         return self::$link;

     }

     //链接数据库的方法

     function connect(){

         $this->db = new mysqli($this->host,$this->user,$this->pwd,$this->database);

         !mysqli_connect_error() or die('连接失败');

         $this->db->query('set names '.$this->charset);

     }

     //执行sql语句的方法

     function query($sql){

         $res = $this->db->query($sql);

         if(!$res){

             echo ("<br />执行失败。");

             echo "<br />失败的sql语句为：" . $sql;

             echo "<br />出错信息为：" . mysqli_error($this->db);

             echo "<br />错误代号为：" . mysqli_errno($this->db);

             die();

         }

         return $res;

     }

     //返回二维数组

     function getAll($sql){

         $res = $this->query($sql);

         return $res->fetch_all();

     }

     //返回字符串

     function getStr($sql){

         $res = $this->query($sql);

         $arr = $res->fetch_all();

         $str = '';

         foreach($arr as $v){

             foreach($v as $vv){

                 $str .= $vv.",";

             }

             $str = substr($str,0,-1);

             $str .= "^";

         }

         $str =  substr($str,0,-1);

         return $str;

     }

     //返回json

     function getJson($sql){

         $res = $this->query($sql);

         $arr = $res->fetch_all();

         return json_encode($arr);

     }

     //返回关联数组

     function getAssoc($sql){

         $res = $this->query($sql);

         $arr = array();

         while($row = $res->fetch_assoc()){

             $arr[$row['department']]=$row;

         }

         return $arr;

     }

 }

 //$config = array(

 //    //'database' => 'mysql'

 //);

 //$DBDA = new DBDA();

 //var_dump($DBDA->getJson('select * from user'));

 //看错误提示

 //$DBDA->query('select * from 123');

 //$res = $DBDA->db->query('select * from user');

 //var_dump($res->fetch_all());

 //禁用了构造方法，直接new会报错。

 //$DBDA = DBDA::getDb();

 //var_dump($DBDA);

 //echo "<br>";

 //$DBDA = DBDA::getDb();

 //var_dump($DBDA);

 <?php

 include('DBDA.class.php');

 $dbda = DBDA::getDb();

 var_dump($dbda->getAll('select * from user'));