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Asked: 2026-05-20T21:27:12+00:00

Why do I get the following text in the referer textbox: Notice: Undefined index:

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Why do I get the following text in the referer textbox:

Notice: Undefined index: referer in
/var/www/register.php on line 86

when the following script loads?

<?php
    error_reporting( E_ALL | E_STRICT );
    ini_set('display_errors', 1);
?>

<html>
    <head>
        <title></title>
        <link rel="icon" type="image/png" href="favicon.ico">

        <?php
            $err = array();

            if( $_SERVER['REQUEST_METHOD']=='POST' ) {

                if( empty( $_POST['display_name'] ) ) $err[] = "display name field is required";
                if( empty( $_POST['email'] ) ) $err[] = "email field is required";
                if( empty( $_POST['password'] ) ) $err[] = "password field is required";

                if( !$err ) {
                    try {
                        $DBH = new PDO( "mysql:host=localhost;dbname=database1", "user", "pass" );
                        $DBH -> setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

                        $STH = $DBH -> prepare( "insert into database1.table1 (display_name, email, password) values ( :display_name, :email, :password )" );

                        $STH -> bindParam( ':display_name', $_POST['display_name'], PDO::PARAM_STR, 100 );
                        $STH -> bindParam( ':email', $_POST['email'], PDO::PARAM_STR, 100 );
                        $STH -> bindParam( ':password', $_POST['password'], PDO::PARAM_STR, 100 );

                        $STH -> execute();

                        if( !empty( $_POST['referer'] ) ) {
                            $STH = $DBH -> prepare( "insert into database1.table2 ( username, status, users_id ) values ( :username, :status, :users_id )" );

                            $strStatus = 1;

                            $STH -> bindParam( ':username', $_POST['display_name'], PDO::PARAM_STR, 100 );
                            $STH -> bindParam( ':status', $strStatus, PDO::PARAM_INT, 1 );
                            $STH -> bindParam( ':users_id', $_POST['referer'], PDO::PARAM_INT, 1 );

                            $STH -> execute();
                        }

                        $DBH = null;

                        header( "Location: ".$_SERVER['PHP_SELF'] );
                        exit;
                    } catch( PDOException $e ) {
                        error_log( $e -> getMessage() );

                        switch( $e -> getCode()) {
                            case 23000:
                                echo "Sorry, the referral ID you have entered does not exist.  However, your account has been created so you can add your referral details in later.";
                                break;
                            default:
                                echo $e -> getMessage();      
                        }
                    }


                } else {
                    foreach( $_POST as $key => $val ) {
                        $form[$key] = htmlspecialchars($val);
                    }
                }
            } else {
                $form['display_name'] = $form['email'] = $form['password'] = '';
            }
        ?>
    </head>

    <body>
        <?php
            if ( isset( $err ) ) {
                foreach( $err as $line ) {
                    echo "<div style=\"error\">".$line."</div>";
                }
            }
        ?>

        <h1>register</h1>

        <form method="post">
            referers id:<br />
            <input type="text" name="referer" value="<?php echo $form['referer']; ?>" /><br /><br />

            name:<br />
            <input type="text" name="display_name" value="<?php echo $form['display_name']; ?>" /><br /><br />

            email:<br />
            <input type="text" name="email" value="<?php echo $form['email']; ?>" /><br /><br />

            password:<br />
            <input type="text" name="password" value="<?php echo $form['password']; ?>" /><br /><br />

            <input type="submit" value="register" />
        </form>
    </body>
</html>
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1 Answer

  1. Editorial Team

    When you are first displaying your form, you are executing this portion of code (line 68) :

    $form['display_name'] = $form['email'] = $form['password'] = '';

    This initializes three items of your $form array, which is why you don’t get notices for those when you try to echo them on lines 89, 92, and 95.

    But the referer item of $form is not initialized.

    So, line 86, when you try to echo it :

    <input type="text" name="referer" value="<?php echo $form['referer']; ?>" /><br /><br />

    You get a notice.

    Two possible solutions :

    • Do not try to echo a variable (or item of an array) that doesn’t exist.
      • The isset() construct can help, to test for that.
    • Or initialize $form['referer'] before trying to use it.
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