php - 未定义索引: topic in C:includes\topic_list.php on line 9 [duplicate]

This question already has answers here:

“Notice: Undefined variable”, “Notice: Undefined index”, and “Notice: Undefined offset” using PHP

(28个答案)


6年前关闭。

            <?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，不确定是什么错误？这可能是错误所在。
if($ topic ['name'] == $ _GET ['topic'] || $ post ['topic_id'] == $ topic ['id']){**

最佳答案

您尝试使用$ _GET ['topic']而不先检查它是否首先存在，这就是为什么会出现该错误的原因。我建议您先使用is_set()或empty()测试变量是否存在。