Re: removing elements while looping with an index, and return values from Set add

[Ken Gosier]

Hello all again. Many thanks for all the replies. I am now using index
remove and not getting the seg faults.

However, I am now having a new problem. I am able to resolve it myself,
but not happy with my solution. Specifically, the removing of elements I
posted yesterday actually takes place in a 2-step loop:


for (i=0; i<2; i++)
{
   id <List> newList = [List create: self];
   id <Index> index = [oldList begin: self];
   id thisElem;

   for (thisElem=[index next]; [index getLoc]==Member;
        thisElem=[index next])
   {
      if (  condition[i]  )
      {
         [newList addLast: [index remove]];
      }
   }
   [index drop];

   ... do stuff with newList ...
}


I first want to get those elements that satisfy condition[0], then those
that satisfy condition[1]. I find that everything goes smashing, wonderful
in the first pass through. But then the second time through, the index
steps off the end of the List, and I get seg faults, b/c messages get sent
to nil id's.

So I re-wrote the code block as:


for (i=0; i<2; i++)
{
   id <List> newList = [List create: self];
   id <Index> index = [oldList begin: self];
   id thisElem;

   fprintf(stderr, "Number of elems in oldList: %d\n",
      [oldList getCount]);

   for (thisElem=[index next]; thisElem != nil;
        thisElem=[index next])
   {
      if (  condition[i]  )
      {
         [newList addLast: [index remove]];
      }
   }
   [index drop];

   ... do stuff with newList ...
}


So I've made 2 changes:
- added in the fprintf(stderr,...) to show me the size of oldList.
- changed the inner for condition from ([index getLoc]==Member) to
(thisElem != nil).

I find that the fprintf statement shows me that oldList has been shortened
after the first pass. And with the second change, I no longer get seg
faults, and the sim runs well.

But like I said, this solution works, but I'm not really happy with it.
Why should the index step off the end of the list after the first
pass-through?

Many thanks again for any help--

-- 
Ken Gosier
address@hidden


                  ==================================
   Swarm-Support is for discussion of the technical details of the day
   to day usage of Swarm.  For list administration needs (esp.
   [un]subscribing), please send a message to <address@hidden>
   with "help" in the body of the message.