PHP - $GLOBALS

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$GLOBALS is one of the "superglobal" or "automatic global" variables in PHP. It is available in all scopes throughout a script. There is no need to do "global $variable;" to access it within functions or methods.

$GLOBALS is an associative array of references to all globally defined variables. The names of variables form keys and their contents are the values of an associative array.

Access Global Variables with $GLOBALS

This example shows $GLOBALS array containing the name and contents of global variables −

<?php
   $var1="Hello";
   $var2=100;
   $var3=array(1,2,3);

   echo $GLOBALS["var1"] . "\n";
   echo $GLOBALS["var2"] . "\n";
   echo implode($GLOBALS["var3"]) . "\n";
?>

Output

It will produce the following outcome −

Hello
100
123

Global vs Local Variables Using $GLOBALS

In the following example, $var1 is defined in the global namespace as well as a local variable inside the function. The global variable is extracted from the $GLOBALS array.

<?php
   function myfunction() {
      $var1="Hello PHP";
      echo "var1 in global namespace: " . $GLOBALS['var1']. "\n";
      echo "var1 as local variable: ". $var1;
   }
   $var1="Hello World";
   myfunction();
?>

Output

It will produce the following result −

var1 in global namespace: Hello World
var1 as local variable: Hello PHP

Modify Global Variables

Prior to PHP version 8.1.0, global variables could be modified by a copy of $GLOBALS array.

<?php
   $a = 1;
   $globals = $GLOBALS; 
   $globals['a'] = 2;
   var_dump($a);
?>

Output

It will produce the below output −

int(1)

Here, $globals is a copy of the $GLOBALS superglobal. Changing an element in the copy, with its key as "a" to 2, actually changes the value of $a.

It will produce the following output −

int(2)

Read-Only $GLOBALS

As of PHP 8.1.0, $GLOBALS is a read-only copy of the global symbol table. That is, global variables cannot be modified via their copy. The same operation as above wont change $a to 2.

<?php
   $a = 1;
   $globals = $GLOBALS; 
   $globals['a'] = 2;
   var_dump($a);
?>

Output

It will generate the following output −

int(1)

Update Global Variables Inside a Function

In the following example, the global variable $counter will be updated directly in the function with the help of $GLOBALS. Each function call increments the value by 1.

<?php
   $counter = 0;

   function incrementCounter() {
      $GLOBALS['counter']++;
   }

   incrementCounter();
   incrementCounter();
   incrementCounter();

   echo "Counter value: " . $counter;
?> 

Output

Following is the output of the above code −

Counter value: 3

Use $GLOBALS in Nested Functions

In the following example, we are using the $GLOBALS inside a nested function. So using this example you can use global variables even inside nested functions.

<?php
   $var = "Hello";

   function outerFunction() {
      function innerFunction() {
         echo $GLOBALS['var'] . " from inner function!";
      }
      innerFunction();
   }

   outerFunction();
?> 

Output

Following is the output of the above code −

Hello from inner function!

Store Arrays in Global Variables

In the following example, the $GLOBALS lets you directly change arrays stored as global variables. The function mentioned in our example adds new items to the array.

<?php
   $var = array("Apple", "Banana");

   function addFruit($fruit) {
      $GLOBALS['var'][] = $fruit;
   }

   addFruit("Orange");
   addFruit("Grapes");

   print_r($var);
?> 

Output

Following is the output of the above code −

Array
(
   [0] => Apple
   [1] => Banana
   [2] => Orange
   [3] => Grapes
)