How to access Topic name from pdfs using poppler?

Question

I am using poppler, and I want to access topic or headings of a particular page number using poppler, so please tell me how to do this using poppler.

Answer 1

Using the glib API. Don't know which API you want.

I'm pretty sure there is no topic/heading stored with a particular page. You have to walk the index, if there is one.

Walk the index with backtracking. If you are lucky, each index node contains a PopplerActionGotoDest (check type!). You can grab the title from the PopplerAction object (gchar *title) and get the page number from the included PopplerDest (int page_num). page_num should be the first page of the section.

Assuming your PDF has an index containing PopplerActionGotoDest objects. Then you simply walk it, checking for the page_num. If page_num > searched_num, go back one step. When you are at the correct parent, walk the childs. This should give you the best match. I just made some code for it:

gchar* getTitle(PopplerIndexIter *iter, int num, PopplerIndexIter *last,PopplerDocument *doc)
{
    int cur_num = 0;
    int next;
    PopplerAction * action;
    PopplerDest * dest;
    gchar * title = NULL;
    PopplerIndexIter  * last_tmp;

    do
    {
            action = poppler_index_iter_get_action(iter);
            if (action->type != POPPLER_ACTION_GOTO_DEST) {
                printf("No GOTO_DEST!\n");
                return NULL;
            }

            //get page number of current node
            if (action->goto_dest.dest->type == POPPLER_DEST_NAMED) {
                dest = poppler_document_find_dest (doc, action->goto_dest.dest->named_dest);
                cur_num = dest->page_num;
                poppler_dest_free(dest);
            } else {
                cur_num = action->goto_dest.dest->page_num;
            }
            //printf("cur_num: %d, %d\n",cur_num,num);

            //free action, as we don't need it anymore
            poppler_action_free(action);

            //are there nodes following this one?
            last_tmp = poppler_index_iter_copy(iter);
            next = poppler_index_iter_next (iter);

            //descend
            if (!next || cur_num > num) {
                if ((!next && cur_num < num) || cur_num == num) {
                    //descend current node
                    if (last) {
                        poppler_index_iter_free(last);
                    }
                    last = last_tmp;
                }
                //descend last node (backtracking)
                if (last) {
                    /* Get the the action and do something with it */
                    PopplerIndexIter *child = poppler_index_iter_get_child (last);
                    gchar * tmp = NULL;
                    if (child) {
                        tmp = getTitle(child,num,last,doc);
                        poppler_index_iter_free (child);
                    } else {
                        action = poppler_index_iter_get_action(last);
                        if (action->type != POPPLER_ACTION_GOTO_DEST) {
                            tmp = NULL;
                        } else {
                            tmp = g_strdup (action->any.title);
                        }
                        poppler_action_free(action);
                        poppler_index_iter_free (last);
                    }

                    return tmp;
                } else {
                    return NULL;
                }
            }

            if (cur_num > num || (next && cur_num != 0)) {
                // free last index_iter
                if (last) {
                    poppler_index_iter_free(last);
                }
                last = last_tmp;
            }
    }
  while (next);

    return NULL;
}

getTitle gets called by:

    for (i = 0; i < num_pages; i++) {
            iter = poppler_index_iter_new (document);
            title = getTitle(iter,i,NULL,document);
            poppler_index_iter_free (iter);

            if (title) {
                printf("title of %d: %s\n",i, title);
                g_free(title);
            } else {
                printf("%d: no title\n",i);
            }
    }