为什么我从PHP获得“Undefined index”？

When I run this code:

当我运行此代码时:

<?php
if (preg_match('/^[a-z0-9]+$/', $_GET['p'])) {
  $page = realpath("includes/$_GET[p].php");
  if ($page) {
    include $page;
  }
}
?>

I get this error:

我收到此错误:

Notice: Undefined index: p in index.php on line 3

注意:未定义的索引:第3行的index.php中的p

6 个解决方案

#1

The error message says that there is no array item with the key p. If you cannot guarantee that a variable (or array item) does exist, you should first check it with the isset function:

错误消息表明没有带键p的数组项。如果您不能保证变量(或数组项)确实存在,则应首先使用isset函数进行检查:

if (isset($_GET['p']) && preg_match('/^[a-z0-9]+$/', $_GET['p'])) {
    $page = realpath("includes/$_GET[p].php");
    if ($page) {
        include $page;
    }
}

#2

What Gumbo said for checking if the index is set in the array.

Gumbo所说的用于检查索引是否在数组中设置。

Also for parsing an array index in a string you should use brackets around the array, and you should escape the index with single quotes if it is a string.

另外,对于解析字符串中的数组索引,您应该在数组周围使用括号,如果是字符串,则应使用单引号转义索引。

$page = realpath("includes/{$_GET['p']}.php");

But for including files suggested by the user, the safest way is to look up the files in an array, and only include them if they exists there.

但是对于包含用户建议的文件,最安全的方法是查找数组中的文件,并且只在它们存在时才包含它们。

#3

$page = realpath("includes/ " . $_GET['p'] . ".php");

#4

There is no real problem. PHP yields a Notice not a Warning or Error. Basically, your script is not receiving the p URL parameter. So it uses '' and gives a notice in the log. If you see this message on your rendered page, adjust php error reporting to something like E_ERROR | E_WARNING in PHP.ini

没有真正的问题。 PHP产生通知而不是警告或错误。基本上,您的脚本没有收到p URL参数。所以它使用''并在日志中发出通知。如果您在渲染页面上看到此消息,请将php错误报告调整为类似E_ERROR |的内容PHP.ini中的E_WARNING

#5

There is no 'p' parameter to the page, maybe? Did you mean $_REQUEST instead?
Also, is it not `"${_GET['p']}" when you are accessing an array?

页面上没有'p'参数,也许?你的意思是$ _REQUEST吗?另外,当你访问一个数组时,它不是“$ {_ GET ['p']}”吗?

#6

Look into array_key_exists() for checking whether an array key... exists. But in your case I suggest you pick up the filter class of functions which specialize in working with user input.

查看array_key_exists()以检查数组键是否存在。但在你的情况下,我建议你选择专门处理用户输入的过滤器类功能。

#1