unset
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
To unset a global variable inside of a function, then 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.
- vars
-
Further variables.
Return Values
No value is returned.
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 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.