Unset a given variable

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- PHP Manual
- Variable handling Functions
- Unset a given variable

# unset

(PHP 4, PHP 5, PHP 7, PHP 8)

unset — Unset a given variable

### Description

unset(mixed `$var`, mixed `...$vars`): void

unset() destroys the specified variables.

The behavior of unset() inside of a function can vary depending on what type of variable you are attempting to destroy.

If a globalized variable is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.

    <?php
    function destroy_foo()
    {
        global $foo;
        unset($foo);
    }

    $foo = 'bar';
    destroy_foo();
    echo $foo;
    ?>

The above example will output:

    bar

To unset() a global variable inside of a function, then use the $GLOBALS array to do so:

    <?php
    function foo()
    {
        unset($GLOBALS['bar']);
    }

    $bar = "something";
    foo();
    ?>

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

    <?php
    function foo(&$bar)
    {
        unset($bar);
        $bar = "blah";
    }

    $bar = 'something';
    echo "$bar\n";

    foo($bar);
    echo "$bar\n";
    ?>

The above example will output:

    something
    something

If a static variable is unset() inside of a function, unset() destroys the variable only in the context of the rest of a function. Following calls will restore the previous value of a variable.

    <?php
    function foo()
    {
        static $bar;
        $bar++;
        echo "Before unset: $bar, ";
        unset($bar);
        $bar = 23;
        echo "after unset: $bar\n";
    }

    foo();
    foo();
    foo();
    ?>

The above example will output:

    Before unset: 1, after unset: 23
    Before unset: 2, after unset: 23
    Before unset: 3, after unset: 23

### Parameters

`var`

  The variable to be unset.

`vars`

  Further variables.

### Return Values

No value is returned.

### Examples

Example #1 unset() example

    <?php
    // destroy a single variable
    unset($foo);

    // destroy a single element of an array
    unset($bar['quux']);

    // destroy more than one variable
    unset($foo1, $foo2, $foo3);
    ?>

Example #2 Using `(unset)` casting

`(unset)` casting is often confused with the unset() function. `(unset)` casting serves only as a `NULL`-type cast, for completeness. It does not alter the variable it's casting. The (unset) cast is deprecated as of PHP 7.2.0, removed as of 8.0.0.

    <?php
    $name = 'Felipe';

    var_dump((unset) $name);
    var_dump($name);
    ?>

The above example will output:

    NULL
    string(6) "Felipe"

### Notes

> Note: Because this is a language construct and not a function, it cannot be called using variable functions, or named arguments.

> Note:

> It is possible to unset object properties visible in the current context.

> If declared, __get() is called when accessing an unset property, and __set() is called when setting an unset property.

> Note:

> It is not possible to unset `$this` inside an object method.

> Note:

> When using unset() on inaccessible object properties, the __unset() overloading method will be called, if declared.

### See Also

- isset() - Determine if a variable is declared and is different than null
- empty() - Determine whether a variable is empty
- __unset()
- array_splice() - Remove a portion of the array and replace it with something else
- (unset) casting