unset

(PHP 4, PHP 5, PHP 7)

unsetUnset 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.

<?phpfunction 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:

<?phpfunction 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.

<?phpfunction 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.

<?phpfunction 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 variableunset($foo);// destroy a single element of an arrayunset($bar['quux']);// destroy more than one variableunset($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.


<?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.

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.

Note:

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

See Also