Error message: Fatal error: Can't use function return > value in write context in - php-5.3

Question

I am trying to run some code from a book. There appears to be a problem with the code.
Here is the error message:
Fatal error: Can't use function return
value in write context in
/Applications/MAMP/htdocs/Eclipse-Workspace/simpleblog/test.php
on line 24
Here is the code referenced in the message (starting on line 24)
if (!empty(trim($_POST['username']))
&& !empty(trim($_POST['email']))) {
// Store escaped $_POST values in variables
$uname = htmlentities($_POST['username']);
$email = htmlentities($_POST['email']);
$_SESSION['username'] = $uname;
echo "Thanks for registering! <br />",
"Username: $uname <br />",
"Email: $email <br />";
}
I would appreciate any help. Please let me know if I need to provide any more information
Thanks a lot guys. That was very fast. The solution works great.
The problem is that the empty() function needs to be applied only to direct variables.
For future reference:
The code is from 'PHP for Absolute Beginners' by Jason Lengstorf (2009), pages 90-91, Chapter 3, $_SESSION
corrected code:
//new - Created a variable that can be passed to the empty() function
$trimusername = trim($_POST['username']);
//modified - applying the empty function correctly to the new variable
if (!empty($trimusername)
&& !empty($trimusername)) {
// Store escaped $_POST values in variables
$uname = htmlentities($_POST['username']);
$email = htmlentities($_POST['email']);
$_SESSION['username'] = $uname;
echo "Thanks for registering! <br />",
"Username: $uname <br />",
"Email: $email <br />";
}

Answer 1

In short: The empty() function only works directly on variables
<?php
empty($foo); // ok
empty(trim($foo)); // not ok
i'd say, for the course of getting further with that book, just use a temporary variable
so change:
if (!empty(trim($_POST['username']))
to
$username = trim($_POST['username']);
if(!empty($username)) {
//....

Answer 2

Exactly your example is mentioned at the manual
Note:
empty() only checks variables as anything else will result in a parse error. In other words, the following will not work: empty(trim($name)).
Use a temporary variable, or just test against "empty string"
if (trim($foo) !== '') {
// Your code
}