An example to use PHP unset to destroy variables

The unset function in PHP

The unset() function is used to clear or destroy the value of a given variable.

To check variable is set or not (assigned a value or not) see PHP isset chapter.

How to use the unset function?

Following is the general syntax of using the PHP unset function:


Example of unset() function

The following example shows how to use the unset function to destroy the value of a variable.

Experience this example online



Notice: Undefined variable: var1 in F:xampphtdocstest.php on line 7

The above program will return a notice in the second call as $var1 is unset.

Uses of unset() function

The unset PHP function can be used to clear session variable values, for example, in a scenario where shopping cart items are stored in the session variables. As a user has completed a transaction, you may want to clear session variables carrying products while still maintaining the user’s id etc.

Scope of unset

The behavior of unsetting a variable in PHP can be different scope wise. For example, if you are destroying a global variable by using the unset() function, it will destroy it only locally.

If a variable is destroyed inside a function, it will be unset only in the context of the rest of the function. The variable will retain the value in other calls.

Further reading: using unset in session variables.

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