$GLOBALS

(PHP 4, PHP 5, PHP 7, PHP 8)

$GLOBALS — References all variables available in global scope

Descrizione

An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array.

Esempi

Example #1 $GLOBALS example

<?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();

?>

Il precedente esempio visualizzerà qualcosa simile a:

$foo in global scope: Example content
$foo in current scope: local variable

Avviso

As of PHP 8.1.0, write access to the entire $GLOBALS array is no longer supported:

Example #2 writing entire $GLOBALS will result in error.

<?php

// Generates compile-time error:
$GLOBALS = [];
$GLOBALS += [];
$GLOBALS =& $x;
$x =& $GLOBALS;
unset($GLOBALS);
array_pop($GLOBALS);
// ...and any other write/read-write operation on $GLOBALS

?>

Note

Nota:
Questa è una variabile 'superglobale', o automaticamente global. Ciò semplicemente significa che è visibile in tutti gli ambiti in uno script. Non è necessario dichiararla come global $variable; per accedervi da funzioni o metodi.

Nota: Variable availability

Unlike all of the other superglobals, $GLOBALS has essentially always been available in PHP.

Nota:
As of PHP 8.1.0, $GLOBALS is now a read-only copy of the global symbol table. That is, global variables cannot be modified via its copy. Previously, $GLOBALS array is excluded from the usual by-value behavior of PHP arrays and global variables can be modified via its copy.
<?php

// Before PHP 8.1.0
$a = 1;

$globals = $GLOBALS; // Ostensibly by-value copy
$globals['a'] = 2;
var_dump($a); // int(2)

// As of PHP 8.1.0
// this no longer modifies $a. The previous behavior violated by-value semantics.
$globals = $GLOBALS;
$globals['a'] = 1;

// To restore the previous behavior, iterate its copy and assign each property back to $GLOBALS.
foreach ($globals as $key => $value) {
    $GLOBALS[$key] = $value;
}

?>

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User Contributed Notes 4 notes

down

inafeeur at gmail dot com ¶

3 years ago

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
?>

down

mstraczkowski at gmail dot com ¶

13 years ago

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";

down

vittorio.zamparella at famous googlemail ¶

9 years ago

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
-------------------------------------

http://www.php.net/manual/en/language.variables.variable.php
-------------------------------------
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.
-------------------------------------

down

therandshow at gmail dot com ¶

15 years ago

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.

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