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.

Example #1 Using unset()

`<?php
function destroy_foo()
{
global $foo;
unset($foo);
}
$foo = 'bar';
destroy_foo();
echo $foo;
?>`

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

Example #2 unset() a Global Variable

`<?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.

Example #3 unset() with Reference

`<?php
function foo(&$bar)
{
unset($bar);
$bar = "blah";
}
$bar = 'something';
echo "$bar\n";
foo($bar);
echo "$bar\n";
?>`

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.

Example #4 unset() with Static Variable

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

### Parameters

`var`

  The variable to be unset.

`vars`

  Further variables.

### Return Values

No value is returned.

### Examples

Example #5 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);
?>`

### 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

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