PHP的登录表格密码无效的消息问题

Question

I have a login form on index.php page, I have a login.php file to connect and check things with MySQL database. If the password or username is wrong, I would like to go back to the form and display an error message.

Currently, the code in login.php after submission is like this:

//database checking...
$num_row = mysql_num_rows($result);
        if( $num_row == 1 ) {
            $_SESSION['login_user']=$username;
            header("location:startscreen.php");                     
        }
        else{
            $_SESSION['login_error'] = "Your username or password is incorrect";
            header("location:index.php");
            exit();
        }

and in the index.php page:

<?php 
if (! empty($_SESSION('login_error'])) {
echo '<div>'.$_SESSION('login_error').'</div>';
}
else {echo '<div>empty error msg</div>';}
?>

Now the situation is: When the password is correct, the page flows correctly, but if the password is wrong, it goes back to the form, but the $_SESSION['login_error'] is actually empty. Is that something obviously wrong here? I can't work out why it didn't work.

Thanks for help!

Answer 1

Add session_start(); on top of your script

And replace your code with the code below in their respective files. This is more efficient way of coding.

login.php

//database checking...
$num_row = mysql_num_rows($result);
if( $num_row ) {
    $_SESSION['login_user']=$username;
    header("location:startscreen.php");                     
} else{
    $_SESSION['login_error'] = "Your username or password is incorrect";
    header("location:index.php");
    exit();
}

index.php

 if ( isset($_SESSION['login_error']) and !empty($_SESSION['login_error']) ) {
        echo '<div>'.$_SESSION('login_error').'</div>';
    } else {
        echo '<div>empty error msg</div>';
    }