array_push（）期望参数1为数组，给定为null

问题描述：

I have the following php code:

<?php

class Session {

    public function __construct() {
        if (!session_id()) {
            session_start();
        }
        if (!is_array($_SESSION['messages'])) {
            $_SESSION['messages'] = [];
        }
        echo is_array($_SESSION['messages']);
    }

    public function AddMessage($msg="") {
        array_push($_SESSION['messages'], $msg);
    }

    public function GetMessages() {
        $messages = $_SESSION['messages'];
        unset($_SESSION['messages']);
        return $messages;
    }

}

$session = new Session();

?>

And the output of $session->AddMessage('message') is:

1 
Warning: array_push() expects parameter 1 to be array, null given in ...\Session.php on line 16

so is_array clearly says that $_SESSION['messages'] IS an array. What am I missing?

我有以下php代码： p>

 ＆lt;？  php 
 
class Session {
 
 public function __construct（）{
 if（！session_id（））{
 session_start（）; 
} 
 if（！is_array（$ _ SESSION ['messages']  ））{
 $ _SESSION ['messages'] = []; 
} 
 echo is_array（$ _ SESSION ['messages']）; 
} 
 
公共函数AddMessage（$ msg =“”）  {
 array_push（$ _ SESSION ['messages']，$ msg）; 
} 
 
公共函数GetMessages（）{
 $ messages = $ _SESSION ['messages']; 
 unset（$ _ SESSION [  'messages']）; 
返回$ messages; 
} 
 
} 
 
 $ session = new Session（）; 
 
？＆gt; 
  code>  pre> \  n 
  $ session-＆gt; AddMessage（'message'）的输出是： p> 
 
 
  1 
警告：array_push（）期望参数1为数组 ，在第16行的\ _ Session.php中给出null; n  code>  pre> 
 
 所以is_array清楚地说$ _SESSION ['messages']是一个数组。
什么是 我错过了？ p> 
   DIV>

答

session_id is a function, so it should be:

    if (!session_id()) { //Not just session_id
        session_start();
    }

If you would have turned on error reporting it might have thrown:

Notice: Use of undefined constant session_id - assumed 'session_id'

Note: OP has edited the original question

array_push（）期望参数1为数组，给定为null

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