Question

运行checklogin.php时出现此错误：

Notice: Undefined variable: username in C:\xampp\htdocs\checklogin.php on line 4

Notice: Undefined variable: password in C:\xampp\htdocs\checklogin.php on line 4

Notice: Undefined variable: db_name in C:\xampp\htdocs\checklogin.php on line 4
cannot select DB

这是checklogin.php的代码

<?php

$host="localhost"; // Host name 
$username=""; // Mysql username 
$password=""; // Mysql password 
$db_name="test"; // Database name 
$tbl_name="members"; // Table name 

// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
mysql_select_db("$db_name")or die("cannot select DB");

// username and password sent from form 
$myusername=$_POST['myusername']; 
$mypassword=$_POST['mypassword']; 

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);

// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){

// Register $myusername, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword"); 
header("location:login_success.php");
}
else {
echo "Wrong Username or Password";
}

我真的不明白这里有什么问题。我很抱歉，如果它显而易见或缺乏任何细节，因为我对此很陌生。

Answer 1

在您的代码第二行中，将用户名设为root

$username="root";

Answer 2

我看不到您收到的通知与提供的源代码之间的关系。

嗯，下次要处理此通知：

1-如果您不确定是否声明变量，请使用：

<?php
if(isset($variable_name))
{
   print $variable_name;
}

2-或者您可以通过使用error_reporting函数来避免通知，在您的情况下，请参阅第2行和第3行：

<?php
// Report all errors except E_NOTICE   
error_reporting(E_ALL ^ E_NOTICE);

$host="localhost"; // Host name 
$username=""; // Mysql username 
$password=""; // Mysql password 
$db_name="test"; // Database name 
$tbl_name="members"; // Table name 

// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
mysql_select_db("$db_name")or die("cannot select DB");

Answer 3

<?php
class DB extends PDO { 

    private $engine; 
    private $host; 
    private $database; 
    private $user; 
    private $pass;      

      private static $instance = NULL;

    public function __construct(){           
        $this->engine = 'mysql'; 
        $this->host = 'localhost'; 
        $this->database = 'test'; //your
        $this->user = 'root'; //your
        $this->pass = '123'; //your
        $dns = $this->engine.':dbname='.$this->database.";host=".$this->host; 
        parent::__construct( $dns, $this->user, $this->pass);       
        $this::__config();      
    }


     static function getInstance()
    {
        if (self::$instance == NULL)
            self::$instance = new DB();
        return self::$instance;
    }


    public function __config(){ //there your config - it's my 
        $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
        $this->query("set character_set_client='utf8'");
        $this->query("set character_set_results='utf8'");      
        $this->query ("SET NAMES utf8");       
    }


} 
?>

在PDO项目中使用此类 $ db = db :: getInstance（）; //致电

用户名，密码和数据库中未定义的变量

3 个答案: