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# unset

(PHP 3, PHP 4, PHP 5)

unset -- Unset a given variable

## Description

void unset ( mixed var [, mixed var [, mixed ...]] )

unset() destroys the specified variables. Note that in PHP 3, unset() will always return `TRUE` (actually, the integer value 1). In PHP 4, however, unset() is no longer a true function: it is now a statement. As such no value is returned, and attempting to take the value of unset() results in a parse error.

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); ?>`

> Note: It is possible to unset even object properties visible in current context.

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

If you would like to unset() a global variable inside of a function, you can 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

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

See also isset(), empty(), and array_splice().

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