error handling - 'At' symbol before variable name in PHP: @$_POST

I've seen function calls preceded with an at symbol to switch off warnings. Today I was skimming some code and found this:

$hn = @$_POST['hn'];

What good will it do here?

Answer

The @ is the error suppression operator in PHP.

PHP supports one error control
operator: the at sign (@). When
prepended to an expression in PHP, any

error messages that might be generated
by that expression will be ignored.

See:

Update:

In your example, it is used before the variable name to avoid the E_NOTICE error there. If in the $_POST array, the hn key is not set; it will throw an E_NOTICE message, but @ is used there to avoid that E_NOTICE.

Note that you can also put this line on top of your script to avoid an E_NOTICE error:

error_reporting(E_ALL ^ E_NOTICE);