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.
Table of Content
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. - Return null from a public function if no result exists.
- Use
null
for properties that may not have a value. - Assign
null
to free up memory or reset a variable. - Set object properties in PHP classes to null by default.
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:
Type | When it Occurs | Example | Check With |
---|---|---|---|
Null | Variable exists but has no value | $var = null; | is_null($var) or $var === null |
Undefined | Variable was never set | $var; | isset($var) (returns false ) |
Empty | Variable has a falsy value | $var = ""; | empty($var) |
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 $stringValue;
Outputs:
(Program did not output anything!)
Wrapping Up
In this tutorial, you learned how PHP handles null
and when to use it. You explored different ways to check for null
:
- Using
is_null()
. - strict comparison (
===
). - Use the
isset()
. - Use the
empty()
.
You also saw the differences between null
–undefined
and empty
values in PHP.
Finally, you learned how to cast null
to other types like integers, strings, arrays, and objects.
Here’s a quick recap:
represents a variable with no value.null
- Use
is_null($var)
or$var === null
to check fornull
. - Use
isset($var)
to check if a variable exists and is notnull
. - Use
empty($var)
to check fornull
and other falsy values. - PHP allows casting
null
into integers, strings, arrays, and objects with type conversion. - In PHP classes, null can be set as default property values.
FAQ’s
What is null in PHP?
-
- It has not been assigned any value.
- It has been explicitly set to null.
- It has been unset using the unset() function.
How can I check if a variable is null in PHP?
$variable = null;
if (is_null($variable)) {
echo "Variable is null";
}
Using strict comparison (===):
$variable = null;
if ($variable === null) {
echo "Variable is null";
}
Using isset() function:
$variable = null;
if (!isset($variable)) {
echo "Variable is null or not set";
}
What is the difference between null, undefined, and empty in PHP?
- null: A variable is null when it has been explicitly assigned null or has not been assigned any value.
- undefined: A variable is considered undefined if it has never been declared or assigned a value. Accessing such a variable will result in a notice-level error.
- empty: A variable is considered empty if it holds a falsy value, such as "" (empty string), 0 (integer zero), 0.0 (float zero), "0" (string zero), false, array() (empty array), or null. The empty() function can be used to check for these values.
How do I set a variable to null in PHP?
$variable = null;
Alternatively, you can use the unset() function to destroy the variable, which will also set it to null:
unset($variable);
How can I cast null to other data types in PHP?
$variable = null;
$intValue = (int) $variable;
echo $intValue; // Outputs: 0
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