<?php

    class DB{

        const HOST='127.0.0.1';

        const USER='root';

        const PASS='root';

        const DATA='mooc';

        static public $_instance;

        private function __construct(){

            mysql_connect(DB::HOST,DB::USER,DB::PASS);

            mysql_set_charset('utf8');

            mysql_select_db(DB::DATA);

        }

        public static function getInstance(){

            if(!self::$_instance instanceof self){

                self::$_instance=new self;

            }

            return self::$_instance;

        }

    }

    $model=DB::getInstance();

    //连接数据库，并且测试

    $sql="select * from user";

    $res=mysql_query($sql);

    while($row=mysql_fetch_assoc($res)){

        var_dump($row);

    }

?>