PHP的致命错误[重复]

Question

我正在做一个管理面板，我正在做一个用于添加用户的表单。我的代码如下：

        <form class="form-horizontal">
<fieldset>

<!-- Form Name -->
<legend>Add user</legend>

<!-- Prepended text-->
<div class="form-group">
  <label class="col-md-4 control-label" for="newuser">Username</label>
  <div class="col-md-4">
    <div class="input-group">
      <span class="input-group-addon">@</span>
      <input id="newuser" name="newuser" class="form-control" placeholder="Username" type="text" required="">
    </div>
    <p class="help-block">Put the new users username here</p>
  </div>
</div>

<!-- Password input-->
<div class="form-group">
  <label class="col-md-4 control-label" for="userpw">New user password</label>
  <div class="col-md-4">
    <input id="userpw" name="userpw" type="password" placeholder="Password" class="form-control input-md" required="">
    <span class="help-block">Enter new user's password here!</span>
  </div>
</div>

<!-- Select Basic -->
<div class="form-group">
  <label class="col-md-4 control-label" for="permissions">Choose permissions</label>
  <div class="col-md-4">
    <select id="permissions" name="permissions" class="form-control">
      <option value="1">System administrator</option>
      <option value="2">Editor</option>
      <option value="3">Developer</option>
      <option value="4">Normal user</option>
    </select>
  </div>
</div>

<!-- Button -->
<div class="form-group">
  <label class="col-md-4 control-label" for="btn_send">Send request to server</label>
  <div class="col-md-4">
    <button id="btn_send" name="btn_send" class="btn btn-primary">Send it!</button>
  </div>
</div>

</fieldset>
</form>
<?php
$newuser = $_GET['newuser']; 
$userpw = $_GET['userpw'];
$permission = $_GET['permissions'];


if(isset($newuser and $userpw and $permission) {
    $sql = "INSERT INTO users(username,userpw,permission)VALUES('$newuser', '$userpw','$permission')";

    mysql_query($sql);
}
else {
echo "error";}

我明白了：

致命错误：无法在 C:\xampp\htdocs\lumino\usermanagement.php 第 95 行的表达式结果上使用 isset()（您可以使用“null !== expression”代替）

无论如何我都无法修复它，玩了大约 5 个小时。 它正在执行 $_GET 方法，所以我得到如下网址：

mysite.com/usermanagement.php?newuser=Berkay&userpw=18042003&permissions=3&btn_send=

Answer 1

使用isset，里面不能有多个项目：

if(isset($newuser and $userpw and $permission) {

需要成为：

if(isset($newuser) && isset($userpw) && isset($permission)) {

或者：

if(isset($newuser, $userpw, $permission)) {

Answer 2

你只是错过了一个)和一组,：

if(isset($newuser, $userpw, $permission)) {
    $sql = "INSERT INTO users(username,userpw,permission)VALUES('$newuser', '$userpw','$permission')";

    mysql_query($sql);
}