Why there is no std::copy_if algorithm?

Question

Is there any specific reason for not having std::copy_if algorithm in C++ ? I know I can use std::remove_copy_if to achieve the required behavior. I think it is coming in C++0x, but a simple copy_if which takes a range, a output iterator and a functor would have been nice. Was it just simply missed out or is there some other reason behind it?

Answer 1

Multiple sources indicate that it was left out of STL by accident.

However, I am not sure if that's a fact or a self-perpetuating myth. I'd appreciate if anyone would point out a source more credible than a link to a random post on the Internet.

Answer 2

According to Stroustrup's "The C++ Programming Language" it was just an over-sight.

(as a citation, the same question answered in boost mail-lists: copy_if)

Answer 3

Stroustrup says they forgot it.

However, you can use remove_copy_if (which really should be called copy_if_not) along with not1 instead.

Answer 4

It's dead easy to write your own:

template <class InputIterator, class OutputIterator, class Predicate>
OutputIterator copy_if(InputIterator first, InputIterator last,
                       OutputIterator result, Predicate pred)
{
  return std::remove_copy_if(first,last,result,std::not1(pred));
}

Edit: This version works with all predicates:

template <class InputIterator, class OutputIterator, class Predicate>
OutputIterator copy_if(InputIterator first, InputIterator last,
                       OutputIterator result, Predicate pred)
{
  while(first!=last)
  {
    if(pred(*first))
        result = *first;
    ++first;
  }
  return result;
}