strip_tags not working

Question

I am truing to filter html characters out like this

$user = $_POST["user"]; //Get username from <form>
mysql_real_escape_string($user); //Against SQL injection
strip_tags($user); //Filter html characters out

But for some reason this is not filtering html characters out. I don't know why, could it by mysql_real_escape_string?

Answer 1

...But, do you mean:

$user = $_POST["user"]; // Get username from <form>
$user = mysql_real_escape_string($user); // Against SQL injection
$user = strip_tags($user); // Filter html characters out

?

As said in the other answers (referring to strip_tags(), but it's the same for mysql_real_escape_string()), these functions do not alter strings directly, but return the modified copy. So you have to assign return values to the same (or another) variable!