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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry role="variable" xml:id="reserved.variables.globals" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>$GLOBALS</refname>
<refpurpose>References all variables available in global scope</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<para>
An associative <type>array</type> containing references to all variables which
are currently defined in the global scope of the script. The
variable names are the keys of the array.
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example xml:id="variable.globals.basic">
<title><varname>$GLOBALS</varname> example</title>
<programlisting role="php">
<![CDATA[
<?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();
?>
]]>
</programlisting>
&example.outputs.similar;
<screen>
<![CDATA[
$foo in global scope: Example content
$foo in current scope: local variable
]]>
</screen>
</example>
</para>
<warning>
<para>
As of PHP 8.1.0, write access to the entire <varname>$GLOBALS</varname> array is no longer supported:
<example xml:id="variable.globals.entire_write_error">
<title>writing entire <varname>$GLOBALS</varname> will result in error.</title>
<programlisting role="php">
<![CDATA[
<?php
// Generates compile-time error:
$GLOBALS = [];
$GLOBALS += [];
$GLOBALS =& $x;
$x =& $GLOBALS;
unset($GLOBALS);
array_pop($GLOBALS);
// ...and any other write/read-write operation on $GLOBALS
?>
]]>
</programlisting>
</example>
</para>
</warning>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
¬e.is-superglobal;
<note>
<title>Variable availability</title>
<para>
Unlike all of the other <link linkend="language.variables.superglobals">superglobals</link>,
<varname>$GLOBALS</varname> has essentially always been available in PHP.
</para>
</note>
<note>
<para>
As of PHP 8.1.0, <varname>$GLOBALS</varname> is now a read-only copy of
the global <link linkend="features.gc.refcounting-basics">symbol table</link>.
That is, global variables cannot be modified via its copy.
Previously, <varname>$GLOBALS</varname> array is excluded from the usual
by-value behavior of PHP arrays and global variables can be modified via its copy.
<informalexample>
<programlisting role="php">
<![CDATA[
<?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;
}
?>
]]>
</programlisting>
</informalexample>
</para>
</note>
</refsect1>
</refentry>
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