As the PHP manual says:
empty — Determine whether a variable is empty
In your case, trim
is a function call, not a variable.
If you really want to do your if
statement inline, you can use something like:
if (!empty($var=trim($_POST['username'])) && !empty($var=trim($_POST['email'])))
But a better implementation should be:
$username = array_key_exists('username', $_POST) ? trim($_POST['username']) : null;
$email = array_key_exists('email', $_POST) ? trim($_POST['email']) : null;
if (!empty($username) && !empty($email))
{
(...)