php unset() destroys single or multiple variables_PHP tutorial-PHP Tutorial-php.cn

The unset function is a function that comes with PHP to destroy variables. We introduced the method of using unset to destroy static variables and global variables. At the same time, we also introduced the method of destroying array variables. Let's see an example below.

Example 1. unset() example

The code is as follows

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代码如下

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// 销毁单个变量
unset ($foo);

// 销毁单个数组元素
unset ($bar['quux']);

// 销毁一个以上的变量
unset ($foo1, $foo2, $foo3);
?>

// Destroy a single variable

unset ($foo);

//Destroy a single array element

代码如下

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function destroy_foo() {
global $foo;
unset($foo);
}

$foo = ‘bar’;
destroy_foo();
echo $foo;
?>

unset ($bar['quux']);

// Destroy more than one variable

unset ($foo1, $foo2, $foo3);

The behavior of unset() in a function will vary depending on the type of variable you want to destroy.

代码如下

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function foo(&$bar) {
unset($bar);
$bar = “blah”;
}

$bar = ‘something’;
echo “$barn”;

foo($bar);
echo “$barn”;
?>
上边的例子将输出：

something
something

If you unset() a global variable in a function, only the local variable will be destroyed, and the variables in the calling environment will maintain the same value before calling unset().

The code is as follows

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function destroy_foo() {

global $foo;

代码如下

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function foo() {
static $b;
$a++;
$b++;
echo "$a---$bn";
unset($a,$b);
var_dump($a);
var_dump($b);
echo "######################n";
}

foo();
foo();
foo();
?>
运行该例子，输出：

1---1
NULL
NULL
#######################
1---2
NULL
NULL
#######################
1---3
NULL
NULL
#######################

unset($foo); } $foo = ‘bar’; destroy_foo(); echo $foo; ?> The above example will output: bar If you unset() a variable passed by reference in a function, only the local variable will be destroyed, and the variables in the calling environment will retain the same value before calling unset().

The code is as follows	Copy code
function foo(&$bar) {<🎜> unset($bar);<🎜> $bar = “blah”;<🎜> }<🎜> <🎜>$bar = ‘something’;<🎜> echo “$barn”;<🎜> <🎜>foo($bar);<🎜> echo “$barn”;<🎜> ?> The above example will output: something something

unset() static variable Strictly speaking, using unset() to destroy a static variable only breaks the reference between the variable name and the variable value. Example:

The code is as follows	Copy code
function foo() {<🎜> static $b;<🎜> $a++;<🎜> $b++;<🎜> echo "$a---$bn";<🎜> unset($a,$b);<🎜> var_dump($a);<🎜> var_dump($b);<🎜> echo "######################n";<🎜> }<🎜> <🎜>foo();<🎜> foo();<🎜> foo();<🎜> ?> Running this example, output: 1---1 NULL NULL ####################### 1---2 NULL NULL ####################### 1---3 NULL NULL #######################

unset() global variable
Like unset() static variables, if you unset() a global variable in a function, only the local variable will be destroyed, and the variables in the calling environment will retain the same value before calling unset().

Try to compare the following two examples:

global $foo;

The code is as follows

代码如下

复制代码

function destroy_foo() {
global $foo;
unset($foo);
}

$foo = 'bar';
destroy_foo();
echo $foo;
?>

function destroy_foo() {
global $foo;
unset($GLOBALS['foo']);
}

$foo = 'bar';
destroy_foo();
echo $foo;
?>

Copy code

function destroy_foo() {

unset($foo);

}

echo $foo;

Running the first example will output: bar , while the second example will not output anything. http://www.bkjia.com/PHPjc/628977.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/628977.htmlTechArticleThe unset function is a function that comes with PHP to destroy variables. We introduced the use of unset to destroy static variables and globals. The variable method can also destroy array variables. Let’s see below...

Related labels：

php unset function variable Multiple us yes of Bring your own destroy

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