PHP unset: How to Unset Variables in Python

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PHP unset Example | unset() Function In PHP Tutorial

To check if the variable is set in PHP, use the PHP isset() function.

PHP unset

PHP unset() is a built-in function that terminates the specified variables. Only a local variable is destroyed if the globalized variable is unset() inside the function.

The variable in the calling context will retain the same value as before unset() was called. If the variable PASSED BY REFERENCE is unset() inside a function, only the local variable is destroyed.

Syntax

The syntax of PHP unset() function is following.

unset (var1, var2.... )

Parameters

You can pass as many variables as possible.

If we want to unset() the global variable inside of the function, then use the $GLOBALS array to do so:

unset($GLOBALS[var]);

See the following code.

<?php

// app.php

$el = 'Millie Bobby Brown';
unset($el);
echo $el;

See the output.

➜  pro php app.php
PHP Notice:  Undefined variable: el in /Users/krunal/Desktop/code/php/pro/app.php on line 5

Notice: Undefined variable: el in /Users/krunal/Desktop/code/php/pro/app.php on line 5
➜  pro

If the static variable is unset() inside the function, unset() destroys the variable only in the context of the rest of the function.

The following calls will restore a previous value of the variable.

<?php

// app.php

function eleven()
{
    static $el;
    $el++;
    echo "Before unset: $el, ";
    unset($el);
    $el = 11;
    echo "after unset: $el\n";
}

eleven();
eleven();
eleven();

See the output.

➜  pro php app.php
Before unset: 1, after unset: 11
Before unset: 2, after unset: 11
Before unset: 3, after unset: 11
➜  pro

PHP unset array

See the following code.

<?php

// app.php

$data = ['Netflix', 'Disney+', 'Comcast', 'HBO GO'];
print_r($data);

unset($data);
print_r($data);

See the output.

➜  pro php app.php
Array
(
    [0] => Netflix
    [1] => Disney+
    [2] => Comcast
    [3] => HBO GO
)
PHP Notice:  Undefined variable: data in /Users/krunal/Desktop/code/php/pro/app.php on line 7

Notice: Undefined variable: data in /Users/krunal/Desktop/code/php/pro/app.php on line 7
➜  pro

Using unset() casting

The unset() casting is often confused with the unset() function.

For completeness, the (unset) casting serves only as the NULL-type cast. It does not alter a variable; it’s casting. The (unset) cast is deprecated as of PHP version 7.2.0.

<?php

$name = 'AppDividend';

var_dump((unset) $name);
var_dump($name);

See the following output.

➜  pro php app.php
PHP Deprecated:  The (unset) cast is deprecated in /Users/krunal/Desktop/code/php/pro/app.php on line 5

Deprecated: The (unset) cast is deprecated in /Users/krunal/Desktop/code/php/pro/app.php on line 5
NULL
string(11) "AppDividend"
➜  pro

PHP unset Cookies

Use the superglobal _COOKIE variable. See the code.

unset($_COOKIE['mycookiename']);

PHP unset session

A session creates the file in the temporary directory on the server where registered session variables and their values are stored.

The data will be available on all pages on the site during that visit.

If you want to destroy the single session variable, you can use the unset() function to unset a session variable. See the code.

<?php
   unset($_SESSION['data']);

That’s it for this tutorial.

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