Xapian discuss - Oct 2006 - having trouble getting position lists from termtierators

I am writing some Cocoa bindings so I can create a graphical "delve"
style
tool for OS X.

I have most of the basic things working off Xapian::Database.

What I am stuck on is I have TermIterator working, but I can't get any
positional information off of terms I _KNOW_ have positional information.
Here is what delve reports.
>delve -t LP:support -r 34 /index/wfs
Position List for term `LP:support', record #34: 12

here is the code I can't get to work, every term throws a
Xapian::InvalidOperationError
begin and end are pointers to copies of the begin and end iterators from
database.
Anyone have a clue what might be going on.


NSMutableArray* terms = [[NSMutableArray alloc] init];
    while (*begin != *end)
    {
        NSString* text = [[NSString alloc]
initWithUTF8String:(**begin).c_str()];

        NSMutableArray* positions = [[NSMutableArray alloc] init];
        try
        {
            Xapian::PositionIterator beginpos = begin->positionlist_begin();
            Xapian::PositionIterator endpos = begin->positionlist_end();
            while (begin != end)
            {
                NSNumber* pos = [NSNumber numberWithUnsignedInt:*beginpos];
                [positions addObject:pos];
                [pos release];
                beginpos++;
            }
        }
        catch ( const Xapian::InvalidOperationError &e )
        {
            NSLog(@"no positions for term %@", text);
        }

On Tue, Oct 31, 2006 at 12:37:12PM -0500, Jarrod Roberson
wrote:
> here is the code I can't get to work, every term throws a
> Xapian::InvalidOperationError
> begin and end are pointers to copies of the begin and end iterators from
> database.
What do you mean by "from database"?

If you're trying to iterate positions from a TermIterator returned by
allterms_begin(), then this is the expected behaviour - there's no
implicit document id context to use to get the positions (a
PositionIterator lists the occurences of a particular term in a
particular document, so a document id and a termname are required).

Note that you can use the termname from the TermIterator and a document
id and use Database::positionlist_begin(did, termname) to create the
PositionIterator.

If this isn't the problem, a compilable example would probably be useful
(ideally without the cocoa parts as the only OS X machines I have access
to are at sourceforge and seem to be offline most of the time).

Cheers,
    Olly