PHP Null: How to Assign and Check for Null Values

PHP introduced null to handle undefined or missing values. It helps prevent errors when you check if a variable exists. Functions can return null when they fail or lack data. Objects can also have null properties if not initialized.

We will cover the following topics in this article:

• Understand how it works in PHP.
• How to check for Null value in PHP.
• Null vs Undefined vs Empty in PHP
• Setting variables to null in PHP.
• How to cast Null in PHP?

Let’s start with how its values work in PHP.

What Is Null in PHP?

PHP null represents a variable with no value. A variable is null if:

• It is not assigned any value.
• It is explicitly set to null.
• Show unset within unset().

PHP treats null as a special type. That means it has no data stored in a variable when it is null.

Here is an example:

$variable = null;

var_dump($variable);

Here is the output:

NULL

You can use null value in the following cases:

• Use null as a placeholder when a value is unknown or optional.
• Functions can return null when no valid result exists.
• Use null for properties that may not have a value.
• Assign null to free up memory or reset a variable.

Let’s move on to the following section to understand how to check for null in PHP.

Check for Null in PHP

PHP provides you multiple ways to check if a variable is null:

• How to use the is_null() built-in function.
• Strict comparison.
• Use the isset().
• Check it within empty().

Let’s take each one in-depth.

Check for Null Within is_null()

The is_null() function returns true if the variable is null.

$variable = null;

if (is_null( $variable )) {  
    echo "Variable is null";  
}

Here is the ouput:

Variable is null

Check for Null Within Strict Comparison

The === operator checks if a variable is exactly null.

$var = null;  
if ($var === null) {  
    echo "Variable is null";  
}

Output:

Variable is null

Use isset()

PHP has isset() the built-in function to check if the is set and not null.

$var = null;  
if ( !isset($var) ) {  
    echo "Variable is null or not set";  
}

The output:

Variable is null or not set

Check Within empty().

The empty() function considers null as empty. It also treats the following values as empty:

• 0
• ""
• false

$var = null;  
if (empty($var)) {  
    echo "Variable is empty or null";  
}

Here is output:

Variable is empty or null

Now lets move on to the below section to see the difference between null, undefined and empty.

Null vs Undefined vs Empty in PHP

PHP has three different concepts for missing or empty values: null, undefined, and empty. Each behaves differently.

Here is a table shows the key differences:

But How to cast null into other types in PHP? In the following section, we will see the answer to that.

How to Cast Null in PHP?

PHP does not allow you to cast null value to other types using (int), (string), (bool), etc. However, you can convert null to other types using explicit casting or type conversion functions.

You can convert null to 0 when cast to an integer.

$var = null;  
$intValue = (int) $var;  
echo $intValue;

Output:

0

Here is another example to cast null value to string.

$var = null;  
$stringValue = (string) $var;  
echo $stringValue; 

Outputs:

(Program did not output anything!)

Wrapping Up

In this tutorial, you learned how PHP handles null and when to use it. You explored different ways to check for null:

• Using is_null().
• strict comparison (===).
• Use the isset().
• Use the empty().

You also saw the differences between null–undefined and empty values in PHP.

Finally, you learned how to cast null to other types like integers, strings, arrays, and objects.

Here’s a quick recap:

• null represents a variable with no value.
• Use is_null($var) or $var === null to check for null.
• Use isset($var) to check if a variable exists and is not null.
• Use empty($var) to check for null and other falsy values.
• PHP allows casting null into integers, strings, arrays, and objects with type conversion.

FAQ’s

  $variable = null;
  if (is_null($variable)) {
      echo "Variable is null";
  }

  $variable = null;
  if ($variable === null) {
      echo "Variable is null";
  }

$variable = null;

unset($variable);

$variable = null;
  $intValue = (int) $variable;
  echo $intValue; // Outputs: 0