Re: how to iterator and delete elements in std::set

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Mon, 22 Nov 2010 09:37:57 -0500

Message-ID:

<icdv87$6v8$1@news.eternal-september.org>

On 11/21/2010 6:36 PM, Leigh Johnston wrote:

On 21/11/2010 23:12, zl2k wrote:

hi, there

Here is what I want to do: I have a set of objects. I need to iterate
each of them to ask if it needs to be eliminated. If yes, I'll erase
it from the set. I don't know which needs to be erased before I touch
it.

std::set<Obj> objs;
...
for (auto obj_iterator = objs.begin(); obj_iterator != objs.end(); +
+obj_iterator){
if (obj_iterator.do_you_want_to_be_erased() == true){
objs.erase(*obj_iterator);
}
}

Now I have the trouble since the iterator is destroyed after the first
erase. What is the proper way to do the job? Thanks.

zl2k

std::set<Obj> objs;
...
for (auto obj_iterator = objs.begin(); obj_iterator != objs.end();){
if (obj_iterator->do_you_want_to_be_erased())
objs.erase(obj_iterator++);
else
++obj_iterator;
}

To expand the answer:

In the new Standard all 'erase' members return the iterator immediately
following the one being erased or 'end()', so with the compliant
compiler you could write

     if (obj_iterator->do_...
         obj_iterator = objs.erase(obj_iterator);
     else
         ++obj_iterator;

(not sure if it's better in any way, though). :-)

V
--
I do not respond to top-posted replies, please don't ask