Which one is better (unset() or $var = null) to free memory in PHP ?

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In this article, we will discuss freeing the memory with unset() and using NULL value to any variable.

unset(): The unset() function is an inbuilt function in PHP that is used to unset a specified variable. The unset() function just destroys or removes the variable from the symbol table. After the unset() applied on a variable, it’s marked for PHP garbage collection.

Syntax:

unset($variable)

$variable which is unset

Example: The following example demonstrates the unset() function. In the following example, the $a memory is removed from the variable stack, the $a does not exist anymore after the unset action.

PHP

<?php 
  
    // Declare a variable and set 
    // to some string 
    $a = "hello zambiatek"; 
    echo "Before unset : $a"; 
          
    // Unset this variable 
    unset($a); 
    echo "<br>"; 
  
    // Display the variable 
    echo "After unset : $a"; 
?> 

Output:

Before unset : hello zambiatek
After unset :

null: null is used to empty the variable. We can create a null variable by simply assigning it to null. The memory is not freed, but NULL data is re-written or re-assigned on that particular variable.

Syntax:

$variable = null;

Example:

PHP

<?php 
  
    // Declare a variable and 
    // set to string 
    $a = "Hello zambiatek"; 
    echo "Before null : $a"; 
          
    // Assign null to this variable 
    $a = null; 
    echo "<br>"; 
  
    // Display result 
    echo "After null : $a"; 
?> 

Output:

Before null : Hello zambiatek
After null :

Which one is better?

unset() function:

unset() does not force immediate memory freeing, and it is used to free variable usage.
PHP garbage collector cleans up the unset variables.
CPU cycles are not wasted
It takes time to free memory

null variable: