QGVector has a write and read method which are called with QDataStream and
the << >> methods.

QVector then inherits these. The documentation for these functions say they
are internal use only.

I think from examples that the number of non null elements of the vector is
written to the stream and then all the the non null elements after. From a
stream the number of elements is read then the elements themselves of which
none are null.

Can anyone confirm this?

Regards

Nick