Datatypes in PHP - NULL : Tutorial

8. NULL data type

Null is a variable with no value. It is called a special data type in PHP.

A variable is null if,

1. It has been assigned the constant NULL
2. It has not been set to any value.
3. It has been unset()

Value NULL is case insensitive.

1. <?php
2. $var = NuLl;
3. echo var_dump($var);
4. 
5. $var1;
6. echo var_dump($var1); //Will throw an Error NULL
7. 
8. echo "<br>";
9. $var2 ="Mike"; 
10. echo var_dump($var2);
11. 
12. unset($var2);
13. echo var_dump($var2); //Will throw an Error NULL   
14. ?>

Output
	

NULL 
Notice: Undefined variable: var1 in E:\xampp\htdocs\xampp\Tutorials\test.php on line 6
NULL 
string(4) "Mike" 
Notice: Undefined variable: var2 in E:\xampp\htdocs\xampp\Tutorials\test.php on line 13
NULL

As we can see $var is defined as NUll (as Null is case insensitive).
$var1 is undefined (variable is declare without assigning value to it is null)
$var2 is defined as Mike and later being uset using unset() function, so it result to null.(this is called as Casting variable to null)