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unset
Unset a given variable
(PHP 4, PHP 5)
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:
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
somethingIf 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: $bar\n";
}
foo();
foo();
foo();
?>The above example will output:
Before unset: 1, after unset: 23
Before unset: 2, after unset: 23
Before unset: 3, after unset: 23Examples
Example 2603. unset() example
<?php
// destroy a single variable
unset($foo);
// destroy a single element of an array
unset($bar['quux']);
// destroy more than one variable
unset($foo1, $foo2, $foo3);
?>
Notes
Because this is a language construct and not a function, it cannot be called using variable functions
It is possible to unset even object properties visible in current context.
It is not possible to unset $this inside an object
method since PHP 5.
| isset() |
| empty() |
| array_splice() |