Xapian discuss - Nov 2008 - Weird problem on PositionIterator

Hi, all,

I just found a weird problem about PositionIterator, and I really hope
somebody could help me out.

My example code looks like the following:

  Xapian::MSetIterator im;
  Xapian::TermIterator it1, it2;
  Xapian::PositionIterator ip1_begin, ip1_end, ip2_begin, ip2_end;

  ip1_begin = db.positionlist_begin(*im, *it1);
  ip1_end = db.positionlist_end(*im, *it1);

  ip2_begin = db.positionlist_begin(*im, *it2);
  ip2_end = db.positionlist_end(*im, *it2);

  for (Xapian::PositionIterator ip1 = ip1_begin; ip1 != ip1_end; ip1++)

  {

          cout << *ip1 << endl;
          for (Xapian::PositionIterator ip2 = ip2_begin; ip2 != ip2_end;
ip2++)
        {
               cout << *ip2 << endl;

         }

  }

Suppose PositionIterator ip1 points to [1 3], andPositionIterator ip2 points
to [2 4], then with the above code it will output:

1

2

4

3

random number

random number

random number

random number

...

and finally end up with a segmentation fault. If I remove one layer of the
loop (either remove layer ip1 or ip2), the program always execture
correctly.  I wonder what I did wrong?

Thanks.

Kevin

On 13/11/2008, zhiguo li <zhiguo.li at gmail.com>
wrote:
>  Xapian::MSetIterator im;
>  Xapian::TermIterator it1, it2;
>  Xapian::PositionIterator ip1_begin, ip1_end, ip2_begin, ip2_end;
I assume there's some initialisation of the above variables which you've
omitted here...
>  ip1_begin = db.positionlist_begin(*im, *it1);
>  ip1_end = db.positionlist_end(*im, *it1);
>
>  ip2_begin = db.positionlist_begin(*im, *it2);
>  ip2_end = db.positionlist_end(*im, *it2);
>
>  for (Xapian::PositionIterator ip1 = ip1_begin; ip1 != ip1_end; ip1++)
>
>  {
>
>          cout << *ip1 << endl;
>          for (Xapian::PositionIterator ip2 = ip2_begin; ip2 != ip2_end;
> ip2++)
The second time around, ip2_begin is no longer valid because PositionIterator is
an input iterator.  You can't factor out ip2_begin and ip2_end like this...

Cheers,
    Olly