PHP is_null

Summary: in this tutorial, you’ll learn how to use the PHP is_null() construct to check if a variable is null.

Introduction to the PHP is_null() construct

PHP is_null() accepts a variable and returns true if that variable is null. Otherwise, it returns false.

is_null(mixed $v): boolCode language: PHP (php)

In this syntax, the $v is the variable to check. If $v doesn’t exist, the is_null() also returns true and issues a notice.

Since the is_null() is a language construct, not a function, you cannot call it via variable functions. For example, the following statement will result in an error:

<?php

$f = is_null;Code language: PHP (php)

However, you can define a function that wraps the is_null() construct like this:

<?php

function isnull($v): bool
{
    return is_null($v);
}Code language: PHP (php)

Alternatively, you can define an arrow function, assign it to a variable, and use that variable function.

<?php

$isnull = fn($v) => is_null($v);

$color = null;
echo $isnull($color); // trueCode language: PHP (php)

PHP is_null() examples

The following example uses the is_null() construct and returns true because the $count variable doesn’t exist:

<?php

var_dump(is_null($count));Code language: PHP (php)

This code also issues a notice:

Notice: Undefined variable: $countCode language: PHP (php)

The following example uses the is_null() and returns true because the $count variable is null:

<?php

$count = null;
var_dump(is_null($count)); // trueCode language: PHP (php)

The following example uses the is_null() and returns false because the $count variable is not null:

<?php

$count = 1;
var_dump(is_null($count)); // falseCode language: PHP (php)

PHP is_null() with array

The following example uses the is_null() to check if the element with the key link is null or not. It returns true because the element doesn’t exist:

<?php

$colors = [
    'text' => 'black',
    'background' => 'white'
];

var_dump(is_null($colors['link']));Code language: PHP (php)

It also returns a notice:

Notice: Undefined index: linkCode language: PHP (php)

PHP is_null() with string index

The following example uses the is_null() to check if the element at index 5 in the string $message is null or not:

<?php

$message = 'Hello';

var_dump(is_null($message[5]));Code language: PHP (php)

It returns false and issues a notice:

PHP Notice:  Uninitialized string offset: 5Code language: PHP (php)

PHP is_null(), equal opeartor (==), and identity operator (===)

The echo displays an empty string for the false value, which is not intuitive. The following defines a function that displays false as the string false instead of an empty string:

<?php

function echo_bool(string $title, bool $v): void
{
    echo $title, "\t", $v === true ? 'true' : 'false', PHP_EOL;
}Code language: PHP (php)

Comparing falsy values with null using equal operator (==)

Comparing a falsy value with null using the equal operator (==) will return true. For example:

The following example compares null with falsy values using the equal operator (==):

<?php

function echo_bool(string $title, bool $v): void
{
    echo $title, "\t", $v === true ? 'true' : 'false', PHP_EOL;
}

echo_bool('null == false:', null == false);
echo_bool('null == 0:', null == 0);
echo_bool('null == 0.0:', null == 0.0);
echo_bool('null =="0":', null == false);
echo_bool('null == "":', null == '');
echo_bool('null == []:', null == []);
echo_bool('null == null:', null == null);Code language: PHP (php)

Output:

null == false:  true
null == 0:      true
null == 0.0:    true
null =="0":     true
null == "":     true
null == []:     true
null == null:   trueCode language: plaintext (plaintext)

Comparing falsy value with null using identity operator (===)

The following example uses the identity operator (===) to compare null with falsy values, only null === null returns true.

<?php

function echo_bool(string $title, bool $v): void
{
    echo $title, "\t", $v === true ? 'true' : 'false', PHP_EOL;
}

echo_bool('null === false:', null === false);
echo_bool('null === 0:', null === 0);
echo_bool('null === 0.0:', null === 0.0);
echo_bool('null ==="0":', null === false);
echo_bool('null === "":', null === '');
echo_bool('null === []:', null === []);
echo_bool('null === null:', null === null);Code language: plaintext (plaintext)

Output:

null === false: false
null === 0:     false
null === 0.0:   false
null ==="0":    false
null === "":    false
null === []:    false
null === null:  trueCode language: PHP (php)

Comparing falsy values with null using the PHP is_null()

The following example uses the is_null() to check if falsy values are null:

<?php

function echo_bool(string $title, bool $v): void
{
    echo $title, "\t", $v === true ? 'true' : 'false', PHP_EOL;
}

echo_bool('is_null(false):', is_null(false));
echo_bool('is_null(0):', is_null(0));
echo_bool('is_null(0.0)', is_null(0.0));
echo_bool('is_null("0"):', is_null("0"));
echo_bool('is_null(""):', is_null(""));
echo_bool('is_null([]):', is_null([]));
echo_bool('is_null(null):', is_null(null));Code language: PHP (php)

Output:

is_null(false): false
is_null(0):     false
is_null(0.0)    false
is_null("0"):   false
is_null(""):    false
is_null([]):    false
is_null(null):  trueCode language: PHP (php)

The is_null() and identity operator (===) return the same result.

Summary

• The is_null() checks a value and returns true if that value is null. Otherwise, it returns false.
• The is_null() behaves the same as the identity operator (===).