php - 未定义索引 : topic in C:includes\topic_list. php 第 9 行

Question

这个问题已经有答案了:

"Notice: Undefined variable", "Notice: Undefined index", "Warning: Undefined array key", and "Notice: Undefined offset" using PHP (29 个回答)

已关闭 9 年前。

            <?php 
                $qr_topic = @mysql_query("SELECT * FROM topics");
                while ($topic = @mysql_fetch_array($qr_topic)) {
                    $highlight = "";
                    **if ($topic['name'] == $_GET['topic'] || $post['topic_id'] == $topic['id']) {**
                        $highlight = "class='highlight'";
                    }
                    echo "<li ".$highlight."><a href='index.php?topic=".$topic['name']."'>".$topic['name']."<img src='img/".$topic['image']."'  width='195' height='90' /></a></li>";
                }
            ?>

出现未定义索引错误，不确定出了什么问题？这可能是错误行。if ($topic['name'] == $_GET['topic'] || $post['topic_id'] == $topic['id']) {**

Answer 1

您尝试使用 $_GET['topic'] 而不首先检查它是否存在，这就是您收到该错误的原因。我建议您首先使用 is_set() 或empty() 测试变量是否存在。