Very perceptive :-). Actually that is the one major feature we are still missing that I would like to add. In fact, a big obstacle to adding random-access type iterators is that I have not yet figured out the right way to design them. It is actually a bit tricky. Here is the problem. In ODBC you have what is called a statement handle, hstmt for short, which holds a handle to a scrollable recordset. The design issue I am struggling with is what happens when you copy an iterator?
Idea 1: Create a new statement handle. This has problems because if you create a new statment handle you will be looking at a different recordset and so may not have exactly the same "position" or set of records which invalidates most random access algorithms. The idea behind scrollable recordsets is that when you crate the statement handle it takes a particular version "snapshot" of the records so that you can work with a consistent set. Idea 2: Use the same statement handle. You can kind of get away with this as long as you are scrolling around within the same buffer of records used by the original iterator. As soon as you leave that buffer you then get into messy issues of how to manage grabbing a new set of records without affecting the old iterator. One way would be to just keep around old buffers but if you have several copies of the iterator pointing to different places this could really start to chew up memory. Anyway, I need to do a bit more research to see if there is a way of working with a copy of a recordset so that I can have multiple copies of an iterator in an efficient way. If you have a suggestion I would be glad to hear it. For input and output iterators the above issue is not a problem, we just create a new statement handle just-in-time if we need it. Input and output iterators don't guarantee a particular order on the records they retrieve. "Bill Seymour" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Corwin Joy wrote: > > > > Just wanted to post a brief note to mention that we have released > > version 3.4 of the C++ Database Template Library. > > > > ... > > > > The website for our free, open source library is: > > http://dtemplatelib.sourceforge.net/index.htm > > > > At first glance, this is very interesting. > > Is there any work going on to support scroll cursors? > The interface could be a kind of read-only random-access > iterator. scrolling_const_select_iterator? > > --Bill Seymour > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost > _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
