Just as an update here, and I hope top posting is de riguer for this
news group,

I solved feature one with xerces getSrcOffset() method. Even though I
had to wrap it with an exception catcher, as the particular version we
are using at work at the moment causes an exception when parsing is
finished (but before the parse method returns) and theres no other way
to find out when its finished.

Feature 2 I dont have a solution for at the moment. DOM is not an
option as the whole point is that a whole file uses up too much memory,
and DOM loads the whole thing at once, thats why we wanted to load in a
section at a time.

If it turns out really important to analyse large files, I will just
have to write a seperate program that uses sax, and maybe only filters
for certain things, or perhaps reparses when people want to "scroll up"
which has its own time trade off for saving memory. Its up to the
customers really. I suspect the real solution is a non-xml indexed
binary format. But the memory issue isnt actually as big as the
customers think it is.. I will work something out.

Boris Kolpackov wrote:
> "Kza" <kzawah@g...> writes:
>
> > Feature 1: A progress display. I have tried a few times now to find a
> > way of asking xerces how far through a file it is in bytes, but no
> > luck. (I did try a per element check, but that involves a whole extra
> > parse at the start just to count the elements). I have tried using the
> > LocalFileInputSource, and getting its BinInputStream and calling itc
> > curPos, but its always 0.
> >
> > Any ideas?
>
> You can implement your own InputStream which will keep track of how
> much data Xerces-C++ has consumed so far. Combine this with the total
> length of the file and you can calculate the progress.
>
>
> > Feature 2: Loading only a "screenful" of the file at a time. I also
> > would like some sort of random access functionality, so if the user
> > scrolls down to 75% of the file, the parser skips forward to that
> > position and starts reading there, and when they scroll back up it goes
> > up and reads just that little bit of the file.
>
> This one would definitely be easier with an in-memory model (e.g., DOM).
>
>
> hth,
> -boris
>
>
> --
> Boris Kolpackov
> Code Synthesis Tools CC
> http://www.codesynthesis.com
> Open-Source, Cross-Platform C++ XML Data Binding