预定义变量
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$_SESSION

$HTTP_SESSION_VARS [已弃用]

$_SESSION -- $HTTP_SESSION_VARS [已弃用] — Session 变量

说明

当前脚本可用 SESSION 变量的数组。更多关于如何使用的信息，参见 Session 函数 文档。

$HTTP_SESSION_VARS 包含相同的信息，但它不是一个超全局变量。 (注意 $HTTP_SESSION_VARS 和 $_SESSION 是不同的变量，PHP 处理它们的方式不同)

更新日志

版本 说明
4.1.0 引入 $_SESSION，弃用 $HTTP_SESSION_VARS。

注释

Note:

“Superglobal”也称为自动化的全局变量。 这就表示其在脚本的所有作用域中都是可用的。不需要在函数或方法中用 global $variable; 来访问它。

参见

预定义变量
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PHP手册
PHP手册 - N: Session 变量

用户评论:

pike-php at kw dot nl (07-Feb-2011 02:00)

When accidently assigning a unset variable to $_SESSION, like

   $_SESSION['foo'] = $bar

while $bar was not defined, I got the following error message:

"Warning: Unknown(): Your script possibly relies on a session side-effect which existed until PHP 4.2.3. Please be advised that the session extension does not consider global variables as a source of data, unless register_globals is enabled. "

The errormessage was quite unrelated and got me off-track. The real error was, $bar was not defined.

Dave (17-Nov-2009 10:05)

If you deploy php code and cannot control whether register_globals is off, place this snippet in your code to prevent session injections:

<?php
if (isset($_REQUEST['_SESSION'])) die("Get lost Muppet!");
?>

charlese at cvs dot com dot au (05-Jul-2009 02:47)

I was having troubles with session variables working in some environments and being seriously flaky in others. I was using $_SESSION as an array. It works properly when I used $_SESSION as pointers to arrays. As an example the following code works in some environments and not others.

<?php
//Trouble if I treate $form_convert and $_SESSION['form_convert'] as unrelated items
$form_convert=array();
if (isset($_SESSION['form_convert'])){
        $form_convert=$_SESSION['form_convert'];
    }
}
?>
The following works well.
<?php
if (isset($_SESSION['form_convert'])){
    $form_convert = $_SESSION['form_convert'];
}else{
    $form_convert = array();
    $_SESSION['form_convert']=$form_convert;
}
?>

bohwaz (31-Aug-2008 10:43)

Please note that if you have register_globals to On, global variables associated to $_SESSION variables are references, so this may lead to some weird situations.

<?php

session_start();

$_SESSION['test'] = 42;
$test = 43;
echo $_SESSION['test'];

?>

Load the page, OK it displays 42, reload the page... it displays 43.

The solution is to do this after each time you do a session_start() :

<?php

if (ini_get('register_globals'))
{
    foreach ($_SESSION as $key=>$value)
    {
        if (isset($GLOBALS[$key]))
            unset($GLOBALS[$key]);
    }
}

?>

Steve Clay (17-Aug-2008 02:28)

Unlike a real PHP array, $_SESSION keys at the root level must be valid variable names.

<?php
$_SESSION[1][1] = 'cake'; // fails

$_SESSION['v1'][1] = 'cake'; // works
?>

I imagine this is an internal limitation having to do with the legacy function session_register(), where the registered global var must similarly have a valid name.

jherry at netcourrier dot com (02-Aug-2008 12:16)

You may have trouble if you use '|' in the key:

$_SESSION["foo|bar"] = "fuzzy";

This does not work for me. I think it's because the serialisation of session object is using this char so the server reset your session when it cannot read it.

To make it work I replaced '|' by '_'.