Php unset () destroys one or more variables

Source: Internet
Author: User

Example 1. unset () example

The code is as follows: Copy code

<? Php
// Destroy a single variable
Unset ($ foo );

// Destroy a single array element
Unset ($ bar ['quux ']);

// Destroy more than one variable
Unset ($ foo1, $ foo2, $ foo3 );
?>

The action of unset () in a function varies depending on the type of the variable to be destroyed.

If unset () is a global variable in the function, only the local variable is destroyed, and the variables in the call environment will keep the same value before the call of unset.

The code is as follows: Copy code

<? Php
Function destroy_foo (){
Global $ foo;
Unset ($ foo );
}

$ Foo = 'bar ';
Destroy_foo ();
Echo $ foo;
?>

The above example will output:

Bar

If unset () is a variable passed by reference in the function, only the local variable is destroyed, and the variables in the call environment will keep the same value before the call of unset.

The code is as follows: Copy code

<? Php
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, the use of unset () to destroy static variables only disconnects the reference between the variable name and the variable value.

Example:

The code is as follows: Copy code

<? Php
Function foo (){
Static $ B;
$ A ++;
$ B ++;
Echo "$ a --- $ bn ";
Unset ($ a, $ B );
Var_dump ($ );
Var_dump ($ B );
Echo "###################### n ";
}

Foo ();
Foo ();
Foo ();
?>
Run this example and output:

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

Unset () global variable
Like the unset () static variable, if unset () is a global variable in the function, only the local variable is destroyed, and the variable in the call environment will keep calling unset () the same value.

Try to compare the following two examples:

The code is as follows: Copy code

<? Php
Function destroy_foo (){
Global $ foo;
Unset ($ foo );
}

$ Foo = 'bar ';
Destroy_foo ();
Echo $ foo;
?>

<? Php
Function destroy_foo (){
Global $ foo;
Unset ($ GLOBALS ['foo']);
}

$ Foo = 'bar ';
Destroy_foo ();
Echo $ foo;
?>


The first example will output bar, while the second example will not have any output.

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