如何将注册系统的错误回显到另一个索引文件

Question

I'm trying to echo registration system errors to the main index.php file, but I'm doing something wrong. Can someone please explain what I've been doing wrong and how to do it right?

index.php file.

<?php 
session_start();
include "config.php"; 

?>

<div class="container">
<h1>Registration</h1>

<?php if(!empty($error)): ?>
<div class="alert alert-danger alert-dismissible">
<ul>
    <li>
        <?php echo $error; ?>
    </li>
</ul>
</div>
<?php endif; ?>

    <button class="close" data-dismiss="alert" aria-label="close">
        <span aria-hidden="true">&times;</span>
    </button>

    <form action="main.php" method="post">
        <p>Username: </p>
        <p><input type="text" name="username" autocomplete="off"></p>
        <p>Password: </p>
        <p><input type="password" name="password" autocomplete="off"></p>
        <p><button name="send" class="btn btn-primary" id="btn">Send</button></p>
    </form>

</div>
</div>

main.php file..

    <?php 
include "config.php";

if(isset($_POST['send'])) {
    $username = $_POST['username'];
    $password = $_POST(md5['password']);

    if(empty($_POST['username'])) {
        $error = "Username is empty<br/>";
    }

    if(empty($_POST['password'])) {
        $error = "Password is empty";
    }

    $query = mysqli_query($connect,"INSERT INTO register(username,password) VALUES('$username', '$password')")
    or die(mysql_error());
    echo "Registred";
}

$_SESSION['error'] = $error;

?>

Answer 1

$error is not defined.

<?php echo $error; ?>

should be

<?php echo $_SESSION['error'];?>

or modify your index.php file as below

<?php 
session_start();
include "config.php"; 
// added this line to your code
$error = (isset($_SESSION['error'])) ? $_SESSION['error'] : "";
?>

<div class="container">
<h1>Registration</h1>

<?php if(!empty($error)): ?>
<div class="alert alert-danger alert-dismissible">
<ul>
    <li>
        <?php echo $error; ?>
    </li>
</ul>
</div>
<?php endif; ?>

    <button class="close" data-dismiss="alert" aria-label="close">
        <span aria-hidden="true">&times;</span>
    </button>

    <form action="main.php" method="post">
        <p>Username: </p>
        <p><input type="text" name="username" autocomplete="off"></p>
        <p>Password: </p>
        <p><input type="password" name="password" autocomplete="off"></p>
        <p><button name="send" class="btn btn-primary" id="btn">Send</button></p>
    </form>

</div>
</div>