$GLOBALS — 引用全局作用域中可用的全部变量
关联数组 array，包含当前脚本内定义成全局范围的所有变量的引用。 数组的键就是变量的名字。
示例 #1 $GLOBALS 范例
<?php
function test()
{
$foo = "local variable";
echo '$foo in global scope: ' . $GLOBALS["foo"] . "\n";
echo '$foo in current scope: ' . $foo . "\n";
}
$foo = "Example content";
test();
?>以上示例的输出类似于：
$foo in global scope: Example content $foo in current scope: local variable
从 PHP 8.1.0 起，不再支持对整个 $GLOBALS 数组的写访问：
示例 #2 写入整个 $GLOBALS 将会导致错误。
<?php
// 生成编译时错误：
$GLOBALS = [];
$GLOBALS += [];
$GLOBALS =& $x;
$x =& $GLOBALS;
unset($GLOBALS);
array_pop($GLOBALS);
// ...以及对 $GLOBALS 的任何其他写入/读写操作
?>注意:
“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 $variable; 来访问它。
注意: 变量可用性
与所有其他超全局变量不同，$GLOBALS在PHP中总是可用的。
注意:
从 PHP 8.1.0 起，$GLOBALS 现在是全局符号表的只读副本。 也就是说，全局变量不能通过副本进行修改。 在之前的版本中，$GLOBALS 数组和 PHP 数组通常传值的行为不一样，全局变量可通过副本修改。
<?php
// PHP 8.1.0 之前
$a = 1;
$globals = $GLOBALS; // 表面意义的按值复制
$globals['a'] = 2;
var_dump($a); // int(2)
// 从 PHP 8.1.0 起
// 这不再修改 $a。先前的行为违反了按值语义。
$globals = $GLOBALS;
$globals['a'] = 1;
// 要恢复以前的行为，请迭代其副本并将每个属性分配回 $GLOBALS。
foreach ($globals as $key => $value) {
$GLOBALS[$key] = $value;
}
?>
We can be more clear with the extension of the given example.
Before PHP Version 8.1
<?php
$a = 1;
$globals = $GLOBALS;
$globals['a'] = 2;
echo $a; // 2
echo $globals['a']; // 2
echo $GLOBALS['a']; // 2
?>
After PHP Version 8.1
<?php
$a = 1;
$globals = $GLOBALS;
$globals['a'] = 2;
echo $a; // 1
echo $globals['a']; // 2
echo $GLOBALS['a']; // 1
?>As of PHP 5.4 $GLOBALS is now initialized just-in-time. This means there now is an advantage to not use the $GLOBALS variable as you can avoid the overhead of initializing it. How much of an advantage that is I'm not sure, but I've never liked $GLOBALS much anyways.Watch out when you are trying to set $GLOBALS to the local variable.
Even without reference operator "&" your variable seems to be referenced to the $GLOBALS
You can test this behaviour using below code
<?php
/**
* Result:
* POST: B, Variable: C
* GLOBALS: C, Variable: C
*/
// Testing $_POST
$_POST['A'] = 'B';
$nonReferencedPostVar = $_POST;
$nonReferencedPostVar['A'] = 'C';
echo 'POST: '.$_POST['A'].', Variable: '.$nonReferencedPostVar['A']."\n\n";
// Testing Globals
$GLOBALS['A'] = 'B';
$nonReferencedGlobalsVar = $GLOBALS;
$nonReferencedGlobalsVar['A'] = 'C';
echo 'GLOBALS: '.$GLOBALS['A'].', Variable: '.$nonReferencedGlobalsVar['A']."\n\n";I finally found information about superglobals not being found in $GLOBALS:
https://bugs.php.net/bug.php?id=65223&edit=2
-------------------------------------
[2013-07-09 12:00 UTC] johannes @php.net
[...]super-globals (aka. auto globals) are not added to symbol tables by default for performance reasons unless the parser sees need. i.e.
<?php
$_SERVER;
print_r($GLOBALS);
?>
will list it. You can also control this using auto_gloals_jit in php.ini: http://www.php.net/manual/en/ini.core.php#ini.auto-globals-jit
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http://www.php.net/manual/en/language.variables.variable.php
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Warning
Please note that variable variables cannot be used with PHP's Superglobal arrays within functions or class methods. The variable $this is also a special variable that cannot be referenced dynamically.
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