STL way of creating/filling std::set from std::vector

Question

I want to create and fill a set from the contents of a member variable of each entry of a vector. This is what I am doing:

struct S { int i; };

int main()
{
    std::vector<S*> structPtrs;

    // code to fill the above vector

    // create set from the above vector
    std::set<int> setInts;
    for (auto it = structPtrs.begin(); it != structPtrs.end(); ++it)
    {
        setInts.insert((*it)->i);
    }
}

Is there an STL way to do it? Or via any available method(s) in <algorithm>?

Answer 1

You can always apply std::transform from the range defined by the vector onto the "range" defined by an std::inserter:

transform(begin(structPtrs), end(structPtrs),
          inserter(setInts, end(setInts)), [] (S* s) {
  return s->i;
});

That should be more than enough use of the standard library.

---

If you are willing to look beyond the standard library, there is also the option of using something like boost::transform_iterator, which will allow you to move the range transformation into the set's initialization:

auto transfomer = [](S* s) { return s->i; };
std::set<int> setInts(
  boost::make_transform_iterator(begin(structPtrs), transfomer),
  boost::make_transform_iterator(end(structPtrs), transfomer)
);