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PHP | unset() Function
  • Last Updated : 09 Apr, 2018

The unset() function is an inbuilt function in PHP which is used to unset a specified variable. The behavior of this function depends on different things. If the function is called from inside of any user defined function then it unsets the value associated with the variables inside it, leaving the value which is initialized outside it.

It means that this function unsets only local variable. If we want to unset the global variable inside the function then we have to use $GLOBALS array to do so.

Syntax

unset($variable)

Parameter

  • $variable: This parameter is required, it is the variable which is needed to be unset

Return Value: This function does not returns any value.



Below programs illustrate the unset() function in PHP:

Program 1:




<?php
  
      $var = "hello";
        
      // No change would be reflected outside
      function unset_value()
      {
          unset($var);
      }
        
      unset_value();
      echo $var;
?>

Outside:

hello

Program 2:




<?php
     
      $var = "hello";
        
      // Change would be reflected outside the function 
      function unset_value()
      {
          unset($GLOBALS['var']);
      }
        
      unset_value();
      echo $var;
?>

Output:

No Output

Program 3:




<?php
      
      // user-defined function
      function unset_value()
      {
          static $var = 0;
          $var++;
            
          echo "Before unset:".$var." ";
            
          unset($var);
      
          // This will create a new variable with
          // existing name
          $var = 5;
           
          echo "After unset:".$var."\n";          
      }
        
      unset_value();
      unset_value();
      unset_value();
      unset_value();
        
?>

Output:

Before unset:1 After unset:5
Before unset:2 After unset:5
Before unset:3 After unset:5
Before unset:4 After unset:5

Note: If a variable is declared static and if it is unset inside the function then, the affect will be in the rest of context of a function only. Above calls outside the function will restore the value.

Reference:
http://php.net/manual/en/function.unset.php

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