php - $_POST not working. "Notice: Undefined index: username..."

So, I am currently learning PHP and was reading on a book about the md5 function for passwords, so I decided to give it a try and see how it goes. I also decided to use the POST method rather than the GET, since I saw people saying that it is safer and doesn't let the variables appearing on the URL.

For my testing project I made a very simple form, which follows:

    
        
        
    
    
        


            











                
                    
                        
Username:
                        
                    
                    
                        
Password:
                        
                    
                
            
            
        
    

The problem is that when I enter the values on BOTH fields and click "Login" I get the following output on the other PHP file.

Notice: Undefined index: username in C:\xampp\htdocs\md5\home\dologin\index.php on line 11
Username non existent

Here follows the code for the "/dologin/index.php" file

    
        

        
    
    
                    mysql_connect("localhost", "root") or die(mysql_error());
            mysql_select_db("test") or die(mysql_error());
            $query = "SELECT password FROM users WHERE username='".$_POST['username']."'";
            $result = mysql_query($query);
            $row = mysql_num_rows($result);
            if(isset($row)){

                $password = (mysql_result($result,$row - 1));
                $enteredpassword = md5("w@#$@#".$_GET['password']."^#3f%#^");
                if($password == $enteredpassword){
                    if(!isset($_COOKIE['PHPSESSID'])){
                        session_start();
                    }
                    $_SERVER['LOGIN_STATUS'] = true;
                } else {
                    die("Access denied");
                }    

            } else {
                die("Username non existent");
            }

        ?>
    

Any help at all on my issue is very much appreciated, thank you for reading.

Answer

undefined index means that somewhere in the $_POST array, there isn't an index (key) for the key username.

You should be setting your posted values into variables for a more clean solution, and it's a good habit to get into.

If I was having a similar error, I'd do something like this:

$username = $_POST['username']; // you should really do some more logic to see if it's set first
echo $username;

If username didn't turn up, that'd mean I was screwing up somewhere. You can also,

var_dump($_POST);

To see what you're posting. var_dump is really useful as far as debugging. Check it out: var_dump