PHP unset() function

The unset() function is a predefined variable handling function of PHP, which is used to unset a specified variable. In other words, "the unset() function destroys the variables".

The behavior of this function varies inside the user-defined function. If a global variable is unset inside a function, the unset() will destroy it locally and leave the same value initially provided for outside. Use the $GLOBALS array to destroy a global variable inside the function.

Note
Note: A variable will not be considered to be set for so long if it is unset using the unset() function.

Syntax

snippet
unset (mixed variable, ….)

Mixed denotes that the parameter can be multiple types.

Parameters

This function accepts one or more parameters, but atleast one parameter must be passed in this function.

variable (required) - This parameter is mandatory to pass as it holds that variable, which is needed to be unset.

… - More number of variables to be unset, which are optional to pass.

Return Values

No value is returned by the unset() function.

Examples

Below some examples are given through which you can understand the working of the unset() function:

Example 1:

snippet
<?php
	//variable $website is initialized
$website='javatpoint.com';
	//display the name of the website
echo 'Before using unset() the domain name of website is : '. $website. '<br>';
	
	//unset the variable $website
unset($website);
//It will not display the name of the website
	echo 'After using unset() the domain name of website is : '. $website;
?>

Output:

Output
Before using unset() the domain name of website is : javatpoint.com Notice: Undefined variable: website in C:\xampp\htdocs\program\unset.php on line 5 After using unset() the domain name of website is :

Example 2: Use of unset()

In this example, we will use the unset() function to destroy the variable. Look at the below example:

snippet
<?php
	$var_value1 = 'test';
	if (isset($var_value1)) {
		//It will print because variable is set
		echo "Variable before unset : ". $var_value1;
		echo "</br>";
		var_dump (isset($var_value1));
	}
	unset ($var_value1);
	echo "</br>Variable after unset : ". $var_value1;
	echo "</br>";
	var_dump (isset($var_value1));
?>

Output:

Output
Variable before unset : test bool(true) Notice: Undefined variable: var_value1 in C:\xampp\htdocs\program\unset.php on line 10 Variable after unset : bool(false)

Example 3: Unset GLOBAL variable, but no changes reflect

If you directly try to unset the global variable inside a function, the changes will be reflected locally, not globally.

snippet
<?php
$var_value1 = "Welcome to javatpoint"; 
        
 // No changes will be reflected outside 
function unset_var_value() 
{ 
          		unset($var_value1); 
      	} 
        
      	unset_var_value(); 
      	echo $var_value1;
?>

Output:

Output
Welcome to javatpoint.

Example 4: Unset global variable when changes reflect

Use the $GLOBAL array to unset a global variable inside a function.

snippet
<?php
$var_value1 = "Welcome to javatpoint"; 
        
      	// Changes will be reflected outside 
    	function unset_var_value() 
      	{ 
          		unset($GLOBALS['var_value1']); 
     	} 
        
      	unset_var_value(); 
      	echo $var_value1;
?>

Output:

Output
Notice: Undefined variable: var_value1 in C:\xampp\htdocs\program\unset.php on line 11

Example 5: Destroy static variable

snippet
<?php
function destroy_var()
	{
		static $var;
		$var++;
		echo "Value before unset: $var, ";
		unset($var);
		$var = 25;
		echo "Value after unset: $var </br>";
	}

	destroy_var();
	destroy_var();
	destroy_var();
?>

Output:

Output
Value before unset: 1, Value after unset: 25 Value before unset: 2, Value after unset: 25 Value before unset: 3, Value after unset: 25
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