PHP: Unset a given variable

Description

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

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

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

Parameters

var: The variable to be unset.
var: Another variable ..
...

Return Values

No value is returned.

ChangeLog

Version Description

4.0.0 unset() became an expression. (In PHP 3, unset() would always return 1).

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);

?>

Notes

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

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

Note: It is not possible to unset $this inside an object method since PHP 5.

unset

Description

Parameters

Return Values

ChangeLog

Examples

Notes

See Also