It is for a column of LineEdits. I need to subclass one (with an index) and then make lots of copies with individual index numbers.
Sounds to me like you are confusing how your program keeps track of multiple QLineEdit instances with the QLineEdit instances themselves. If you simply stick the QLineEdit pointers into a vector as you create them, then the index in the vector -is- the index of the QLineEdit. If all of your QLineEdit instances are connected to the same slot, then you can use the QObject::sender() method in the slot to get the pointer to the specific QLineEdit instance that sent the signal, and then search the vector to get the index.

Or if your "index" is non-sequential, you can make a QMap< QWidget *, int > to map the QLineEdit pointer to any integer.

Or you can use QSignalMapper to associate each QLineEdit instance with an integer.

There are lots of ways to do what I think you are trying to do without having to make a custom widget.