[Xapian-discuss] TermIterator question

[Olly Betts]

On 13/11/2008, zhiguo li <zhiguo.li at gmail.com> wrote:
> I would like to have two term iterators to go over the list of terms like
> the following:
>
> for (t1 = query.get_terms_begin(); t1 != query.get_terms_end(); t1++)
>
>       for (t2=t1+1; t2 != query.get_terms_end(); t2++)
>
> {
>
>    do something terms pointed by t1 and t2...
>
> }
>
> When I tried the above, I got error since I cannot perform t2 = t1 + 1 or t2
> = ++t1.

You can't useful copy a TermIterator like this, since it what the C++ STL terms
an "input iterator" - advancing it invalidates any copies at the old position.

Instead write the inner loop as:

    TermIterator t2 = query.get_terms_begin();
    t2.skip_to(*t1);
    if (t2 != query.get_terms_end()) ++t2;
    for ( ; t2 != query.get_terms_end(); ++t2) {
        // ...
    }

Or take a copy of the terms in your own data structure and work from that.

Cheers,
    Olly