PHP 手冊
上一頁 |  | 下一頁

# unset

(PHP 3, PHP 4, PHP 5 )

unset -- Unset a given variable

## Description

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

unset() destroys the specified variables. Note that in PHP 3, unset() will always return `TRUE` (actually, the integer value 1). In PHP 4, however, unset() is no longer a true function: it is now a statement. As such no value is returned, and attempting to take the value of unset() results in a parse error.

示範 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); ?>`

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 would output:

    bar

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 would output:

    something
    something

If a static variable is unset() inside of a function, unset() destroys the variable and all its references.

`<?php function foo() { static $a; $a++; echo "$a\n"; unset($a); } foo(); foo(); foo(); ?>`

The above example would output:

    1
    2
    3

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(); ?>`

> 備注:由於這是一個語言結構、而不是函數，所以不能以變數函數的方式來呼叫。

See also isset(), empty(), and array_splice().

上一頁 | 最開頭 | 下一頁
unserialize | 上一層 | var_dump