Check if Input was filled, if not - continue with script

[PHPstarter]

Hiya. I have a script that is run by a <form> which basically allows u to write into inputs the fields username, new username, password, repeat password, comment etc,

The problem is that I want the script to work in a way that, if a field, like the 'new username' has not been touched (no value), then the username wont be changed.

The same kind of rule would go for the other inputs, so that only parts of a user can be edited at a time, without affecting other data.

Im using this script:

// EDIT USERNAEME
 
 if ((strlen($username)!==0)||(UserInDB($_POST["username"])))
   //if(empty($_POST["newusername"]))
   {
    if (!(UserInDB($_POST["newusername"])))
     {
        mysql_query("UPDATE Users SET login='".$_POST["newusername"]."' WHERE login='".$username."'");
        $oldname=$_POST["username"];
        $newname=$_POST["newusername"];
        echo $user_edited_name=' <b> The user <font color="#FFFFFF"><u>" '.$oldname.' "</u></font> was renamed to <font color="#FFFFFF"><u>" '.$newname.' "</u></font> in the user database.</b> ';
        //echo '<meta http-equiv="Refresh" content="2; url=index.php"> ';
     }
   }

where

 if ((strlen($username)!==0)||(UserInDB($_POST["username"])))

Is supposed to check if the field newusername has been used,
and the function

if (!(UserInDB($_POST["newusername"])))

Checks if the user (from input "username") exists in the database.

The only problem is that the 'check if field was used' string doesnt work at all. If I want to update a different field, like "comment", I only input the username and leave newusername empty, but the user still gets renamed into " " (nothing).
You also see signs of trying the empty() function, which didnt help.
At least not how I tried it.


So how do I fix this?
Thanks

[code green]

Where does $username come from

if ((strlen($username)!==0

Do you have register globals switched on?
It looks like if $username is empty.

[PHPstarter]

Oh yeah, how silly. That could be the error.

Edit: I checked my file and I actually have $username defined at the top, because it is used other places in the script.

I'm very new to PHP still, so could it be some character or symbol error in there?

This error is something that also occurs for different fields, like 'comment'.
So I cant simply update individual data on a user, since it just updates with the empty fields.

I really need some help to fix this :(

[kovik]

You are using "empty()" inside of your failing if-statement...

Using empty() is like checking if the variable is set and if it is non-empty and nonzero. The data you are checking is from a posted form, right? Then you only need to check in the $_POST array.

First, check if the $_POST array is non-empty. If so, then the form has been submitted. Secondly, check for the entry in the $_POST array that you are interested in. If it is non-empty, then it was successfully filled and submitted.

Also, $username should have no effect on the outcome, so I'm not sure why you are checking it...