注意:串联时未定义的变量 [英] Notice : Undefined variable when concatenating

问题描述

我一直在制作脚本来显示用户并更改其管理员权限.

I have been making a script to display users and make changes to their admin privileges.

这是代码:

    while ($row= mysql_fetch_assoc($query)) {
    $uname= $row['username'];
    $fname= $row['first_name'];
    $lname= $row['last_name'];
    $email= $row['email'];
    $admin= $row['admin'];

    $insert .= '<tr>
    <td>' .$uname. '</td>
    <td>' .$fname. '</td>
    <td>' .$lname. '</td>
    <td>' .((isset($email)) ? $email:'No email set.'). '</td>
    <td>'.(($admin == 'y') ? 'Admin':'User').'</td>
    <td><input type="checkbox" name="' .$uname. '" value="'.(($admin == 'y')?'n':'y').'"/>'.(($admin == 'y')?'Make a user':'Make an admin user').'</tr>';
    }   

然后在html中稍后使用$ insert变量生成带有用户数据的所有表行.

The $insert variable is then used later in the html to generate all the table rows with the user data.

问题在于，当我运行脚本时，会显示此消息

The problem is that when I run the script this message appears

    Notice: Undefined variable: insert in C:\wamp\www\...\user_edit.php on line 33

尽管该脚本仅在页面中间显示此消息，但脚本仍然可以正常工作.

The script still works correctly though with only this message showing in the middle of the page.

当我拿的时候.从$ insert.='部分消失，消息消失了，但是脚本仅在表中显示一个用户.

When I take the . off from the $insert .= ' part the message disappears but the script only displays one user in the table.

有什么原因可能会发生这种情况吗?而且我的问题有解决方案吗，这样我才能使脚本正常工作并且消息不出现?

Is there any reason why this may be happening? And is there a solution to my problem so I can have the script working and the message not showing up?

推荐答案

在使用变量之前，只需将其设置为空字符串即可.您不能在尚不存在的变量上使用.=:

Just set the variable to an empty string before you use it. You can't use .= on a variable that does not exist yet:

$insert = "";
while($row= mysql_fetch_assoc($query)) {
    // ...
    $insert .= '<tr>';
    // ...

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