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Null

Description

The null type is PHP’s unit type, i.e. it has only one value: null.

Undefined, and unset() variables will resolve to the value null.

– PHP Reference

Example: null type

<?php

$someNothing = null;

print("Information:\n");
var_dump($someNothing);
print('Type: ' . gettype($someNothing) . PHP_EOL);
print("As string: {$someNothing}\n");

Result (PHP 8.4):

Information:
NULL
Type: NULL
As string:

Source code: Example

Syntax

There is only one value of type null, and that is the case-insensitive constant null.

<?php
$var = NULL;
?>

– PHP Reference

PHP keywords are case-insensitive. Therefore, NULL is also case-insensitive. It means that you can use null, Null, or NULL to represent the null value. For example:

<?php

$email = null;
$first_name = Null;
$last_name = NULL;

It’s a good practice to keep your code consistent. If you use null in the lowercase in one place, you should also use it in your whole codebase.

– PHP Tutorial

Example: Null syntax and case sensitivity

<?php

$someNothing = null;
$otherNothing = NULL;
$anotherNothing = Null;

print("null: ");
var_dump($someNothing);

print("NULL: ");
var_dump($otherNothing);

print("Null: ");
var_dump($anotherNothing);

Result (PHP 8.4):

null: NULL
NULL: NULL
Null: NULL

Source code: Example

Usage

Example: Undefined value use case

<?php

$user = [
    'name' => null,
    'age' => 30,
    'email' => null
];

if ($user['name'] === null) {
    echo "Username is missing.\n";
} else {
    echo "Welcome, " . $user['name'] . ".\n";
}

Result (PHP 8.4):

Username is missing.

Source code: Example

Example: Database query with no result use case

<?php

function findUserById($id) {
    $users = [
        1 => 'Alice',
        2 => 'Bob'
    ];

    return $users[$id] ?? null;
}

$user = findUserById(999);

if ($user === null) {
    echo "User not found.\n";
} else {
    echo "User: $user" . PHP_EOL;
}

Result (PHP 8.4):

User not found.

Source code: Example

Testing for null

To check if a variable is null or not, you use the is_null() function. The is_null() function returns true if a variable is null; otherwise, it returns false. For example:

Example: Testing for null

<?php

$email = null;
var_dump(is_null($email)); // bool(true)

$home = 'phptutorial.net';
var_dump(is_null($home)); // bool(false)

To test if a variable is null or not, you can also use the identical operator ===. For example:

<?php

$email = null;
$result = ($email === null);
var_dump($result); // bool(true)

$home= 'phptutorial.net';
$result = ($home === null);
var_dump($result); // bool(false)

– PHP Tutorial

Example: Testing for null

<?php

$someNothing = null;

print('Type of nothing: ' . gettype($someNothing) . PHP_EOL);
print('Is null? ' . (is_null($someNothing) ? 'yes' : 'no') . PHP_EOL);
print('Is null? ' . (($someNothing === null) ? 'yes' : 'no') . PHP_EOL . PHP_EOL);

$someValue = 10;

print('Type of value: ' . gettype($someValue) . PHP_EOL);
print('Is null? ' . (is_null($someValue) ? 'yes' : 'no') . PHP_EOL);
print('Is null? ' . (($someValue === null) ? 'yes' : 'no') . PHP_EOL . PHP_EOL);

Result (PHP 8.4):

Type of nothing: NULL
Is null? yes
Is null? yes

Type of value: integer
Is null? no
Is null? no

Source code: Example

Casting to null

Warning

This feature has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this feature is highly discouraged.

Casting a variable to null using (unset) $var will not remove the variable or unset its value. It will only return a null value.

– PHP Reference

Example: Null as unset effect

<?php

$someValue = 10;

print("Some value: ");
var_dump($someValue);

unset($someValue);

print("Some value after unset: ");
var_dump($someValue);
// PHP Warning:  Undefined variable $someValue

Result (PHP 8.4):

Some value: int(10)
Some value after unset: PHP Warning:  Undefined variable $someValue on line 11
NULL

Source code: Example

Casting from null

Example: Casting from null

<?php

$someNothing = null;

$toBool = (bool) $someNothing;
print("To bool: ");
var_dump($toBool);
print(PHP_EOL);

$toInteger = (int) $someNothing;
print("To integer: ");
var_dump($toInteger);
print(PHP_EOL);

$toFloat = (float) $someNothing;
print("To float: ");
var_dump($toFloat);
print(PHP_EOL);

$toString = (string) $someNothing;
print("To string: ");
var_dump($toString);
print(PHP_EOL);

$toArray = (array) $someNothing;
print("To array:\n");
var_dump($toArray);
print(PHP_EOL);

$toObject = (object) $someNothing;
print("To object:\n");
var_dump($toObject);
print(PHP_EOL);

Result (PHP 8.4):

To bool: bool(false)

To integer: int(0)

To float: float(0)

To string: string(0) ""

To array:
array(0) {
}

To object:
object(stdClass)#1 (0) {
}

Source code: Example

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