PHP Variable Scope

PHP Variable Scope

PHP variables can be declared anywhere in the PHP code.

The scope of a variable is the part of the script where the variable can be referenced/used.

PHP has three different variable scopes:

• global
• local
• static

Global Scope

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:

$x = 5; // global scope

function myTest() {
  // using x inside this function will not work
  echo "Variable x inside function is: $x";
}
myTest();

echo "Variable x outside function is: $x";

Local Scope

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function.

Local variables are created when the function is called and are destroyed when the function finishes executing:

function myTest() {
  $x = 5; // local scope
  echo "Variable x inside function is: $x";
}
myTest();

// using x outside the function will not work
echo "Variable x outside function is: $x";

Static Scope

Normally, when a function finishes executing, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job. To achieve this, use the static keyword when you first declare the variable.

Then, each time the function is called, that variable will have the value from the last time the function was called.

Note: The variable is still local to the function.

function myTest() {
  static $x = 0; // static scope
  echo $x;
  $x++;
}

myTest();
myTest();
myTest();

PHP global Keyword

The global keyword is used to access a global variable from within a function.

To do this, use the global keyword before the variables (inside the function):

$x = 5;
$y = 10;

function myTest() {
  global $x, $y;
  $y = $x + $y;
}

myTest();
echo $y; // outputs 15

PHP $GLOBALS Superglobal

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.

The example above can be rewritten like this:

$x = 5;
$y = 10;

function myTest() {
  $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}

myTest();
echo $y; // outputs 15