blocks|key|661454|text|就在while之前，您设置了变量$passwordRetrieved，因此它应该如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|661455|$tUser_SQLselect_Query+=+mysql_query($tUser_SQLselect);
$passwordRetrieved+=+"";


while+($row+=+mysql_fetch_array($tUser_SQLselect_Query,+MYSQL_ASSOC))+{
++++$passwordRetrieved+=+$row['password'];
}|code-block|syntax|javascript|661456|entityMap^0|2|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Just before <code>while</code> where you set variable $passwordRetrieved declare it so it should look like this:

<pre><code>$tUser_SQLselect_Query = mysql_query($tUser_SQLselect);
$passwordRetrieved = "";


while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
 $passwordRetrieved = $row['password'];
}
</code></pre>

blocks|key|661388|text|这是因为您的查询没有返回任何内容，而|type|unstyled|depth|inlineStyleRanges|entityRanges|data|661389|while+($row+=+mysql_fetch_array($tUser_SQLselect_Query,+MYSQL_ASSOC))+{|offset|length|style|CODE|661390|不填|661391|$passwordRetrieved|661392|您可以禁用E_NOTICE通知，因为它不会造成伤害|661393|或添加|661394|$passwordRetrieved+=+"";|code-block|syntax|javascript|661395|在你的|661396|while+($row+=+mysql_fetch_array($tUser_SQLselect_Query,+MYSQL_ASSOC))+{|661397|entityMap^0|0|0|1Z|0|0|0|I|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|14|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|15|8|@$D|16|E|17|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|18|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|19|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1A|8|@]|9|@]|A|$S|T]]|$1|U|3|V|5|6|7|1B|8|@]|9|@]|A|$]]|$1|W|3|X|5|R|7|1C|8|@]|9|@]|A|$S|T]]|$1|Y|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|Z|$]]

That's because your query returned nothing and your 

<code>while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {</code> 

didn't fill 

<code>$passwordRetrieved</code>

You can disable E_NOTICE notices because it's not something that would hurt

Or add 

<pre><code>$passwordRetrieved = "";
</code></pre>

before your 

<pre><code>while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
</code></pre>

blocks|key|659391|text|while+($row+=+mysql_fetch_array($tUser_SQLselect_Query,+MYSQL_ASSOC))+{
++$passwordRetrieved+=+$row['password'];
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|659392|这是唯一可以将值赋值给变量$passwordRetrieved的地方。|unstyled|offset|length|style|CODE|659393|如果结果集中没有记录，则不会执行while-循环的主体，因此不会将值分配给$passwordRetrieved，因此在第39行->+Notice:+Undefined+variable:+passwordRetrieved+in+C:\wamp\www\loginForm.php+on+line+39中不存在/未定义$passwordRetrieved。|659394|entityMap^0|0|D|I|0|11|I|1U|2D|4F|I|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@$G|Q|H|R|I|J]]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@$G|T|H|U|I|J]|$G|V|H|W|I|J]|$G|X|H|Y|I|J]]|9|@]|A|$]]|$1|M|3|-4|5|F|7|Z|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
 $passwordRetrieved = $row['password'];
}
</code></pre>

this is the only place where a value may be assigned to the variable <code>$passwordRetrieved</code>. 
If there is no record in the result set the body of the while-loop is never executed and therefore no value ever is assigned to <code>$passwordRetrieved</code> and therefore <code>$passwordRetrieved</code> does not exist/is undefined at line 39 -> <code>Notice: Undefined variable: passwordRetrieved in C:\wamp\www\loginForm.php on line 39</code>.

blocks|key|661415|text|当变量$passwordRetrieved尚未被赋予值时，您将尝试访问它。访问在这里完成：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|661416|echo+"passwordRetrieved+=+".$passwordRetrieved."<br+/>";|code-block|syntax|javascript|661417|变量将设置在上面：|661418|while+($row+=+mysql_fetch_array($tUser_SQLselect_Query,+MYSQL_ASSOC))+{
++++$passwordRetrieved+=+$row['password'];++//+VARIABLE+SET+HERE
}|661419|重要的是，只有当查询返回匹配的行(即在成功登录时)，变量才会被设置。如果登录无效，则不会设置变量。|661420|要检查变量是否设置而没有得到通知，您可以使用isset或empty+(两者之间有细微的差别，但根据经验规则，您可以在大部分时间使用)。实际上，您的代码已经在下面这样做了：|661421|//+Checking+if+$passwordRetrieved+has+been+set+using+empty()
if+(!empty($passwordRetrieved)+AND+($password+==+$passwordRetrieved))+{|661422|entityMap^0|3|I|0|0|0|0|0|M|5|S|5|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|S|3|T|5|H|7|18|8|@]|D|@]|E|$I|J]]|$1|U|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|V|$]]

You are trying to access the variable <code>$passwordRetrieved</code> when it has not yet been given a value. The access is done here:

<pre><code>echo "passwordRetrieved = ".$passwordRetrieved."&lt;br /&gt;";
</code></pre>

The variable would be set just above:

<pre><code>while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
 $passwordRetrieved = $row['password']; // VARIABLE SET HERE
}
</code></pre>

The important thing is that the variable only gets set if the query returns a matching row (i.e., on a successful login). If the login is not valid, the variable is not set.

To check if a variable is set without getting a notice, you would use either <code>isset</code> or <code>empty</code> (there are subtle differences, but as a rule of thumb you can use either most of the time). Your code actually already does this just below:

<pre><code>// Checking if $passwordRetrieved has been set using empty()
if (!empty($passwordRetrieved) AND ($password == $passwordRetrieved)) {
</code></pre>

blocks|key|2332341|text|如果您的查询没有返回任何结果，那么$passwordRetrieved是未定义的(正如消息所述)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2332342|当您找不到任何使用username=$username的用户时，您应该抛出一个错误(这也是一个无效的登录)。|2332343|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

If your query returned no results, then $passwordRetrieved is undefined (just like the message says).

You should throw an error when you couldn't find any users with username=$username (which is also an invalid login).

blocks|key|659410|text|您只需使用一个未定义的变量。如果您的while循环不能工作，那么变量steel是未定义的，因此您获得了一个错误:)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|659411|entityMap^0|I|5|Y|5|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

You simply use an undefined variable. If your <code>while</code> loop doesn't work your variable <code>steel</code> is undefined, so you obtain an error :)

blocks|key|2332409|text|使用mysql_num_rows($result)进行一次检查，以确保您确实得到了一些东西。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2332410|entityMap^0|2|N|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Do a check using <code>mysql_num_rows($result)</code> to make sure you actually got something.

blocks|key|659437|text|您应该在使用$passwordRetrieved之前定义它。这个通知一点也不影响它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|659438|为了避免这种情况，请定义它：|659439|$thisScriptName+=+"loginForm.php";

$passwordRetrieved;|code-block|syntax|javascript|659440|entityMap^0|6|I|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

You should define <code>$passwordRetrieved</code> before using it. This notice does not affect it at all.

To avoid this, define it:

<pre><code>$thisScriptName = "loginForm.php";

$passwordRetrieved;
</code></pre>

blocks|key|2332441|text|由于这个问题已经得到了回答，我还可以添加而不是在MYSQL_ASSOC参数中使用mysql_fetch_assoc()+:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2332442|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

As this question has already been answered, I would also add instead of using mysql_fetch_array with the MYSQL_ASSOC parameter, you can just use mysql_fetch_assoc() :)

I'm doing some exercises from Beginners PHP &amp; MySQL by Mr. Tucker.

On his example everything works fine, but on my PC there is an error:

<blockquote>
 Notice: Undefined variable: passwordRetrieved in C:\wamp\www\loginForm.php on line 39
</blockquote>

Full PHP code for this example:

<ul>
<li>Please note the table does exist, and password, connection to the DB, etc... are correct

<pre><code>&lt;?php
 {
 // Secure Connection Script
 include('htconfig/dbConfig.php');

 $dbSuccess = false;
 $dbConnected = mysql_connect($db['hostname'], $db['username'], $db['password']);

 if ($dbConnected) {
 $dbSelected = mysql_select_db($db['database'], $dbConnected);
 if ($dbSelected) {
 $dbSuccess = true;
 }
 }
 // END Secure Connection Script
 }

 $thisScriptName = "loginForm.php";

 echo '&lt;h2&gt;Login Form &lt;/h2&gt;';

 $username = $_POST['username'];

 if(isset($username)) {
 $password = $_POST['password'];
 echo "username = " . $username . "&lt;br /&gt;";
 echo "password = " . $password . "&lt;br /&gt;";

 {
 // SELECT password for this user from the DB and see it it matches
 $tUser_SQLselect = "SELECT password FROM tUser ";
 $tUser_SQLselect .= "WHERE username = '" . $username . "' ";

 $tUser_SQLselect_Query = mysql_query($tUser_SQLselect);
 while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
 $passwordRetrieved = $row['password'];
 }
 mysql_free_result($tUser_SQLselect_Query);

 echo "passwordRetrieved = ".$passwordRetrieved."&lt;br /&gt;";

 if (!empty($passwordRetrieved) AND ($password == $passwordRetrieved)) {

 echo "YES. Password matches.&lt;br /&gt;&lt;br /&gt;";
 echo '&lt;a href="' . $thisScriptName . '"&gt;Logout&lt;/a&gt;';
 }
 else {
 echo "Access denied.&lt;br /&gt;&lt;br /&gt;";
 echo '&lt;a href="' . $thisScriptName . '"&gt;Try again&lt;/a&gt;';
 }
 }
 }
 else {

 echo '&lt;form name="postLoginHid" action="' . $thisScriptName . '" method="post"&gt;';
 echo '
 &lt;P&gt;User name:
 &lt;INPUT TYPE=text NAME=username value=""&gt;&lt;/P&gt;
 &lt;P&gt;Password:
 &lt;INPUT TYPE=password NAME=password value=""&gt;&lt;/P&gt;
 &lt;input type="submit" value="Login" /&gt;
 ';
 echo '&lt;/form&gt;';
 }

 echo '&lt;h2&gt;--------- END Login Form --------&lt;/h2&gt;';
?&gt;
</code></pre></li>
</ul>

PHP - Undefined variable

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

教程

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云智能顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

EdgeOne AI 安全实战专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

聚焦“写作效率、视觉美观与运行性能”三方面进行全面升级，为您提供更高效、稳定的创作环境

社区富文本&Markdown编辑器全新改版上线，欢迎大家体验!

诚挚邀请您参与本次调研，分享您的真实使用感受与建议。您的反馈至关重要，感谢您的支持与参与！

社区新版编辑器体验调研

我正在做一些由塔克先生编写的初学者PHP & MySQL的练习。在他的例子中，一切都很好，但是在我的PC上有一个错误：注意:未定义变量:第39行C:\wamp\www\loginForm.php中的passwordRetrieved此示例的完整PHP代码：请注意该表确实存在，密码、数据库连接等.是正确的

问PHP -未定义变量
EN

回答 9

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问PHP -未定义变量EN

回答 9

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问PHP -未定义变量
EN