What does undefined index mean?

[asmith6]

I've tried multiple mysql tutorials thus far and some of them, have codes like this:

$Page = $_GET["BLAH"];

if(!$_GET["BLAH"])

, I get an error of "Notice: Undefined Index: BLAH" in the file location and line number.

 

Does anybody know what undefined index means and how I can patch up the problem? Thanks!

[trq]

Undefined index means exactly what it says. The index "BLAH" does not yet exist within the $_GET array.

 

You need to check for it's existence before attempting to use it's value.

 

if (isset($_GET['BLAH'])) {
  // safe to use
}