Question

php连接数据库 提示：no database selected

有三个文件。config.php , mysql.class.php, connect.php...
config.php 定义了连接数据库的常量：
<?php
define('DB_HOST','localhost');
define('DB_USER_NAME','yduser');
define('DB_PASSWORD','12345');
define('DB_DATABASE','hlj');
define('DB_CONN','pconn');
define('DB_CONN_SET','UTF8');

mysql.class.php 中设置了连接数据库的方式
<?php
class mysql{

private $db_host; //数据库主机
private $db_user; //数据库用户名
private $db_pwd; //数据库用户名密码
private $db_database; //数据库名
private $conn; //数据库连接标识;

/*构造函数*/
public function construct($db_host,$db_user,$db_pwd,$db_database,$conn,$coding){
$this->db_host=$db_host;
$this->db_user=$db_user;
$this->db_pwd = $db_pwd;
$this->db_database=$db_database;
$this->conn=$conn;
$this->coding=$coding;
$this->connect();
}
/*数据库连接*/
public function connect()
{
if($this->conn=="pconn"){
$this->conn=mysql_pconnect($this->db_host,$this->db_user,$this->db_pwd);
}else{
$this->conn=mysql_connect($this->db_host,$this->db_user,$this->db_pwd);
}
if(!mysql_select_db($this->db_database,$this->conn)){
if($this->show_error){
$this->show_error("Error",mysql_error());
exit();
}
}
mysql_query("SET NAMES $this->coding");
}
===========connect.php 中实例化mysql类，
require('./config.php');
require('./mysql.class.php');
$conobj =new mysql(DB_HOST,DB_USER_NAME,DB_PASSWORD,DB_DATABASE,DB_CONN,DB_CONN_SET);
$con=$conobj->connect();
if($con){
echo "数据库连接成功";
}else{
echo "数据库连接失败";

运行的时候出现no database selected ，调试显示常量值没有传递到函数中，请问该怎么办？

Answer 1

两种可能，要么没连上，要么不存在hij数据库
if(!mysql_select_db($this->db_database,$this->conn))上面添加一行来判断是否连上

if (!$this->conn)
{
die('Could not connect: ' . mysql_error());
}

追问

用了您的代码，排除了连接上的问题，可是hlj数据库也是存在的。。。。

追答

if(!mysql_select_db($this->db_database,$this->conn)){
if($this->show_error){
$this->show_error("Error",mysql_error());
exit();
}
}
这段代码有问题，show_error没有定义，函数也没定义，改为下面那样
if(!mysql_select_db($this->db_database,$this->conn)){
die('Could not connect: ' . mysql_error());
}