Php/docs/function.unset
unset
(PHP 4, PHP 5, PHP 7)
unset — Unset a given variable
Description
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 alanguage 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
- isset() - Determine if a variable is declared and is different than NULL
- empty() - Determine whether a variable is empty
- __unset()
- array_splice() - Remove a portion of the array and replace it with something else
- (unset) casting