PHP NULL

In PHP, a variable with no value is said to be of null data type. Such a variable has a value defined as NULL. A variable can be explicitly assigned NULL or its value can be set to null by using the unset() function.

Syntax

$var = NULL;

It is possible to cast a variable of other type to null, although casting null to other type has been deprecated from PHP 7.2. In earlier versions, casting was done using (unset)$var syntax.

Example

Following example shows how to assign NULL to a variable ?

<?php
$var = NULL;
var_dump($var);
?>

NULL

Type Casting from NULL

The following example demonstrates casting a null variable to other primary data types ?

<?php
$var = NULL;
var_dump((int) $var);
var_dump((float) $var);
var_dump((bool) $var);
var_dump((string) $var);
?>

int(0)
float(0)
bool(false)
string(0) ""

Using unset() Function

You can also create NULL values using the unset() function ?

<?php
$name = "John";
echo "Before unset: ";
var_dump($name);

unset($name);
echo "After unset: ";
var_dump($name);
?>

Before unset: string(4) "John"
After unset: NULL

Checking for NULL Values

Use is_null() function to check if a variable is NULL ?

<?php
$var1 = NULL;
$var2 = "";
$var3 = 0;

var_dump(is_null($var1)); // true
var_dump(is_null($var2)); // false
var_dump(is_null($var3)); // false
?>

bool(true)
bool(false)
bool(false)

Conclusion

NULL represents the absence of a value in PHP. It can be assigned directly, created with unset(), and checked using is_null(). When cast to other types, NULL converts to empty or false values.