PHP unset() function

Author：Eve Cole Update Time：2024-12-28 10:24:01

The unset() function is used to destroy the given variable.

PHP version requirements: PHP 4, PHP 5, PHP 7

grammar

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

Parameter description:

$var: variable to be destroyed.

return value

No return value.

Example

<?php // Destroy a single variable unset ( $foo ) ; // Destroy a single array element unset ( $bar [ ' quux ' ] ) ; // Destroy more than one variable unset ( $foo1 , $foo2 , $foo3 ) ; ?>

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

Example

<?php function destroy_foo ( ) { global $foo ; unset ( $foo ) ; } $foo = ' bar ' ; destroy_foo ( ) ; echo $foo ; ?>

The output is:

bar

If you want to unset() a global variable in a function, you can use the $GLOBALS array:

Example

<?php function foo ( ) { unset ( $GLOBALS [ ' bar ' ] ) ; } $bar = " something " ; foo ( ) ; ?>

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

Example

<?php function foo ( & $bar ) { unset ( $bar ) ; $bar = " blah " ; } $bar = ' something ' ; echo " $bar n " ; foo ( $bar ) ; echo " $bar n " ; ?>

The above routine will output:

 somethingsomething

If you unset() a static variable in a function, the static variable will be destroyed inside the function. However, when this function is called again, this static variable will be restored to the value it had before it was last destroyed.

Example

<?php function foo ( ) { static $bar ; $bar ++; echo " Before unset: $bar , " ; unset ( $bar ) ; $bar = 23 ; echo " after unset: $bar n " ; } foo ( ) ; foo ( ) ; foo ( ) ; ?>

The above routine will output:

 Before unset: 1, after unset: 23Before unset: 2, after unset: 23Before unset: 3, after unset: 23