Feature Request: possibility to know that QIODevice is in error state

Using QtIOCompressor, QBuffer etc and there is an error, it's impossible to know from within the program. errorString reports "Unknown Error" also when no error has occurred.

Update: Because the errors can only occur in relation to the user calling open, read or write, and all these functions can return an error (i.e., false, 0 or -1), you do know when an error occurs, but there's no way of finding out why programmatically. You can use errorString() to display the error in a log, as console output or in a dialog, though.