是否登录判断

                    <div class="d-none d-lg-block nav-subsidiary">
                        <div class="d-flex justify-content-between text-nowrap">
                            <a class="btn btn-outline-primary" href="<?= BLOG_URL ?>?keyword">
                                <i class="bi bi-search me-1"></i>搜索
                            </a>
                            <?php if (_g('displayLoginBtn')): ?>
                                <?php if (ISLOGIN == 1): ?>
                                    <a class="btn btn-outline-primary btn-action-account ms-lg-3" href="<?= BLOG_URL ?>admin/">
                                        <i class="bi bi-box-seam me-1"></i>管理
                                    </a>
                                    <a class="btn btn-outline-primary btn-action-account ms-lg-3" href="<?= BLOG_URL ?>admin/account.php?action=logout">
                                        <i class="bi bi-arrow-bar-right me-1"></i>退出
                                    </a>
                                <?php else: ?>
                                    <a class="btn btn-outline-primary btn-action-account ms-lg-3" href="<?= BLOG_URL ?>admin/account.php?action=signin">
                                        <i class="bi bi-person me-1"></i>登录
                                    </a>
                                <?php endif; ?>
                            <?php endif; ?>
                        </div>
                    </div>

<?php if(isset($_SESSION['user_id'])): ?>
    <!-- 用户已登录，显示的内容 -->
    <p>欢迎您，<?php echo $_SESSION['user_name']; ?>！</p>
    <a href="<?php echo Url::logout(); ?>">退出登录</a>
<?php else: ?>
    <!-- 用户未登录，显示的内容 -->
    <p>您还没有登录，请<a href="<?php echo Url::logout(); ?>">登录</a>或者<a href="<?php echo Url::login(); ?>">注册</a>。</p>
<?php endif; ?>