PHP Variable Scopes

Summary: in this tutorial, you’ll learn about PHP variable scopes, which specify the part of code that can access a variable.

Introduction to PHP variable scopes #

The scope of a variable determines which part of the code can access it. The locations where the variable can be accessible determine the scope of the variable.

In PHP, variables have four types of scopes:

• Local
• Global
• Static
• Function parameters

Local variables #

When you define a variable inside a function, you can only access that variable within the function. The variable is said to be local to the function.

The following example defines the say() function that displays the 'Hi' message:

<?php

function say()
{
	$message = 'Hi';
	echo $message;
}Code language: PHP (php)

Inside the say() function, we define the $message variable. The $message variable is a local variable. And you cannot access it from the outside of the say() function.

Also, the $message variable only exists during the execution of the say() function. Once the say() function ends, the $mesage variable won’t exist anymore.

Global variables #

When you declare a variable outside of a function, the variable is global. You can access the variable anywhere within the script except inside a function. For example:

<?php

$message = 'Hello';

function say()
{
	$message = 'Hi';
	echo $message;
}

echo $message; // HelloCode language: PHP (php)

Try it

In this script, we have two variables with the same name $message.

The first is the global variable because we define it outside a function. The $message variable that we define inside the function is the local variable. Even though these variables have the same name, they’re different.

PHP allows you to access a global variable within a function by using the global keyword. For example:

<?php

$message = 'Hello';

function say()
{
	global $message;
	echo $message; // Hello
}

say();Code language: PHP (php)

Try it

How it works.

• First, define a global variable called $message.
• Second, reference the global variable $message inside the say() function.

It’s important to note that using global variables is not a good practice.

Superglobal variables #

PHP has a list of built-in variables known as superglobal variables. These variables provide information about the PHP script’s environment.

The superglobal variables are always available in all parts of the script. The following table shows the list of  PHP superglobal variables:

Static variables #

A static variable retains its value between function calls. Also, a static variable is only accessible inside the function. To define a static variable, you use the static keyword. For example:

<?php

function get_counter() {
    static $counter = 1;
    return $counter++;
}

echo get_counter() .  '<br>'; // 1
echo get_counter() .  '<br>'; // 2
echo get_counter() .  '<br>'; // 3Code language: PHP (php)

Try it

Output:

1
2
3Code language: plaintext (plaintext)

How it works.

• First, define the get_counter() function with a static variable named $counter. 
• Second, call the set_counter() function three times. As you notice the value of the $counter variable is increased by one after each function call.

Function parameters #

Function parameters are local to the function. Therefore, function parameters can only be accessible inside the function. For example:

<?php 

function sum($items) {
    $total = 0;
    foreach($items as $item) {
        $total += $item;
    }
    return $total;
}

// $items cannot be accessible here
echo sum([10,20,30]);Code language: PHP (php)

Try it

In this example, the $items is the parameter of the sum() function. It can only be accessible within the sum() function.

Summary #

• PHP has four types of variable scopes including local, global, static, and function parameters.