Re: [Boost-users] erase and iterators

From: bringiton bringiton (kneeride_at_[hidden])
Date: 2006-07-11 03:31:23

Yes, I didn't like the step back. esp since if the first element was
deleted, the iterator would step out of vector memory (ie position -1).

Mike, I do like your remove_if example.

i am not familar with this approach, can you please give me an example of
defining a some_condition_functor? for example when the value == 5.

On 7/11/06, Michael Nicolella <boost_at_[hidden]> wrote:
>
>  vec.erase( std::remove_if( vec.begin(), vec.end(), some_condition_functor
> )  );
>
> or:
>
> for( std::vector<T>::iterator it = vec.begin(); it != vec.end() )
> {
>    if( some_condition )  it = vec.erase(it);
>    else ++it;
> }
>
>
> the key here is that erase() returns the next valid iterator. "Stepping
> back" like that isn't correct - after you call erase on that iterator, it's
> invalidated. The first method above is usually preferred, the second works
> but is less efficient.
>
> FYI I coded this within the email, so there may be something wrong...
>
> Mike
>
>
>  ------------------------------
> *From:* bringiton bringiton [mailto:kneeride_at_[hidden]]
> *Sent:* Monday, July 10, 2006 11:56 PM
> *To:* boost-users_at_[hidden]
> *Subject:* [Boost-users] erase and iterators
>
>
>
> is this common practise for using an interator with erase? what i wish to
> do is interate through each item and delete the item if some condition is
> true.  when i delete, i need to move back a step so that i dont miss an
> item.
>
> for (std::vector<int>::iterator it = vect.begin(); it != vect.end(); it++)
> {
>  if ((*it) == 5) { // some condition
>   vect.erase(it);
>   it--; //  step back
>  }
> }
>
> or would it be best to use a reverse iterater? (or possible?)
>
> for (std::vector<int>::reverse_iterator it2 = vect.rbegin(); it2 !=
> vect.rend(); it2++) {
>  if ((*it) == 5) {
>   // i'm not actually sure how to erase with a reverse iterator???
>   vect.erase(it2);
>  }
> }
>
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