删除Cookie后，PHP回显的导航栏项未出现

Question

我做了一个简单的注册/登录脚本。它确实运行良好，但是现在，我无法显示HTML标签（锚标签）。在我实施删除Cookie之前，该方法已经奏效。这是我的导航代码：

<div class="nav-wrapper z-depth-1">
   <a href="index.php" class="brand-logo center">Todo <i class="material-icons right">add_circle_outline</i></a>
   <h6 id="loginName" class="valign-wrapper"><?php echo "Eingeloggt als: ". $_COOKIE['user']; ?></h6>
   <?php
      if(!isset($_COOKIE["user"])){
          echo '<a href="register.php" class="right" id="register">Registrieren</a><a href="login.php" class="right" id="login">Einloggen</a>';
      }else {
          echo '<a href="logout.php" class="right" id="logout">Ausloggen</a>';
      }
      ?>
</div>

成功登录后，我设置了cookie：

 if (isset($_POST["username"]) && isset($_POST["password"]))
    {
    $username = $_POST["username"];
    $password = $_POST["password"];

    $sql = "SELECT username FROM user WHERE username = :feldwert";
    $kommando = $db->prepare($sql);
    $wert = $username;
    $kommando -> bindParam(':feldwert', $wert);
    $kommando -> execute();
    if($kommando->rowCount() > 0){
        echo "Benutzer existiert!";
        $sql = "SELECT username, password FROM user WHERE username ='".$username."';";
        $erg = $db->query($sql);

        foreach ($erg as $row){
            $user = $row["username"];
            $pass = $row["password"];

            if(password_verify($password, $pass)){
                setcookie("user", $user, time() + 60*60*12);
                header("Location: index.php");

            }else {
                echo "Falschen Benutzernamen oder Passwort eingegeben!";
            }
        }

我的注销脚本如下：

<?php

setcookie("user","", 0);
header("Location: index.php");

?>

即使这不会删除cookie，我还是手动将其删除（或像使用firefox-addon一样），仍然没有定位标记。