在AtomicReference getAndSet和其他此类方法中，字段valueOffSet的作用是什么(What is role of field valueOffSet in AtomicReference getAndSet and other such methods)

 你的问题很常见。 
 
 许多学习者无法从包含四个字母“NULL”的字符串中分辨出NULL值。 而后者绝对没有特殊意义。 
 
 还有一个坏消息：HTTP协议是基于文本的。 意味着使用HTTP方法不能发送除字符串之外的任何内容，因此无法通过HTTP POST发送NULL值。 
 
 要使此代码有效，您必须在服务器端添加NULL，就像您为密码所做的那样： 
 
function post($POST)
{   
   $POST = array_map('trim', $_POST);
   $hash = "$2y$10$";
   $salt = "nekiludistringzahash22";
   $his = $hash . $salt;
   $POST['pass'] = crypt($_POST['pass'],$his);
   $POST['reg_time'] = NULL;
   $POST['id'] = NULL;
   return $POST;  
}
 
 但是，这不是您的代码的主要问题。 最糟糕的消息是你的代码非常容易受到sql注入的攻击 ，尽管看似正确的绑定。 
 
 为了使其安全，请使您的函数接受允许字段列表 ，并为缺少的字段分配NULL值： 
 
function post($allowed)
{   
    $post = array();
    foreach ($allowed as $key)
    {
       if (isset($_POST[$key])) $post[$key] = trim($_POST[$key]);
       else $_POST[$key] = NULL;
   }
   $hash = "$2y$10$";
   $salt = "nekiludistringzahash22";
   $his = $hash . $salt;
   $POST['pass'] = crypt($_POST['pass'],$his);
}
 
 然后像这样调用它： 
 
$post = post(array('id','uname','pass','name','lname','reg_time'));
$sql = "insert into users values(:" . implode(",:", array_keys($post)).");";
$reg = $db->prepare($sql);
$reg->execute($post);
 
 这样您就可以过滤掉所有字段名称。 
 
 作为奖励，您将能够为提交按钮分配自定义值;） 

Your problem is quite common. 
 
Many learners cannot tell a NULL value from a string that consists of four letters "NULL". While the latter has absolutely no special meaning. 
 
And also there are bad news: HTTP protocol is text-based. Means one cannot send anything but a string using an HTTP method, and thus a NULL value cannot be sent over HTTP POST.
 
To make this code work, you have to add your NULLs at the server side, just like you are doing it for the password:
 
function post($POST)
{   
   $POST = array_map('trim', $_POST);
   $hash = "$2y$10$";
   $salt = "nekiludistringzahash22";
   $his = $hash . $salt;
   $POST['pass'] = crypt($_POST['pass'],$his);
   $POST['reg_time'] = NULL;
   $POST['id'] = NULL;
   return $POST;  
}
 
However, it is not the main problem with your code. The worst news is that your code is severely vulnerable to sql injection, despite the seemingly proper binding. 
 
To make it safe, make your function accept the list of allowed fields, and assign a NULL value to absent ones:
 
function post($allowed)
{   
    $post = array();
    foreach ($allowed as $key)
    {
       if (isset($_POST[$key])) $post[$key] = trim($_POST[$key]);
       else $_POST[$key] = NULL;
   }
   $hash = "$2y$10$";
   $salt = "nekiludistringzahash22";
   $his = $hash . $salt;
   $POST['pass'] = crypt($_POST['pass'],$his);
}
 
And then call it like this:
 
$post = post(array('id','uname','pass','name','lname','reg_time'));
$sql = "insert into users values(:" . implode(",:", array_keys($post)).");";
$reg = $db->prepare($sql);
$reg->execute($post);
 
this way you will have all the field names filtered out.
 
As a bonus, you'll be able to assign a custom value to your submit button ;)