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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.

Пример 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
();


?>

Замечание: Поскольку это языковая конструкция, а не функция, она не может вызываться при помощи переменных функций

Смотрите также isset(), empty(), and array_splice().

Все функции PHP: