isset

isset is intended to check if a variable exists or if it is not null. That being the case, isset makes perfect sense in developing an application in PHP.

Imagine the following scenario: You need to know if a given value was passed in the url via parameter GET . To find out if this value exists, you need to use the isset function.

See:

if (isset($_GET['page'])) {
   $page = $_GET['page'];
   require __DIR__ . '/pages/' . $page . '.php';
}

In the above example, if you tried to capture the variable $_GET['page'] directly, without checking the existence of that index before, you would cause an error similar to that to be omitted if the page was omitted in the url:

  

Notice: undefined index "page"

Read more at:

When do I need to use the isset?

unset

The unset function in turn is intended to remove a variable. Its usage is less common than isset .

It is only intended to remove a variable, so that it no longer exists.

I do not have a practical example, but you could use, for example, a variable that holds a file name that has just been deleted. If it has just been deleted, you no longer need its name.

Then

 $arquivo = 'dir/nome_do_arquivo.txt';

 unlink($arquivo);

 unset($arquivo);