Re: [gnugo-devel] sgf/sgfnode.c possible error

[Paul Pogonyshev]

Dmitri Koulikov wrote:

>   I've found a controversial usage of 'parent' link of SGFNode in
> functions sgfPrev and sgfAddChild by one side and sgfStartVariant and
> sgfStartVariantFirst by the other. The first ones use it always as a
> pointer to the parent node while the latter use it to show to the
> previous sibling if it exist and to the parent if not.
>   Where is the truth?

I cannot understand what you mean.  The structure of an SGF tree
inside GNU Go looks like this:

  parent node
       |
 (first) child --> next (child) --> next (child) --> NULL

So, the childs form a single-linked list.  Since you cannot go
directly backwards in a single-linked list, you need to start
from the list beginning and skip forward.  In other words,
previous node can be found like this:

  if (node->parent) {
    previous = node->parent->child;
    while (previous->next != node)
      previous = previous->next;
  }

Paul