php - How to check whether a variable in $_GET Array is an integer?

Question

I have a page like so:

http://sitename/gallery.php?page=2

It has pagination links at the bottom by which we can browse. Everytime the page numbers are clicked, it would send a GET request with parameters page=1 or page=2 and so on ...

When I store these values to $page from teh $_GET variable, it is a string value. I can convert it to an integer using (int) like this:

if(!empty($_GET['page'])){
       $page = (int)$_GET['page'];
       echo "Page Number: ".$page;
}

But how can I make sure that the value passed is an integer only and not other crap?

Answer 1

Using filters:

if (null !== ($page = filter_input(INPUT_GET, 'page', FILTER_VALIDATE_INT, FILTER_NULL_ON_FAILURE))) {
    // $page is now an integer
}

This also checks whether the variable appears in the query string at the same time. If you want to differentiate between missing and invalid you have to leave off the last argument to filter_input():

$page = filter_input(INPUT_GET, 'page', FILTER_VALIDATE_INT);
// $page can be null (not present), false (present but not valid) or a valid integer