Efficiently moving contents of std::unordered_set to std::vector

问题

In my code I have a std::unordered_set and I need to move the data into a std::vector. I'm using the std::unordered_set while getting the data to ensure only unique values are stored prior to converting to a std::vector. My question is how do I move the contents to the std::vector the most efficiently? I don't need the std::unordered_set after the data is moved. I currently have the following:

std::copy(set.begin(), set.end(), std::back_inserter(vector));

回答1:

Before C++17, the best you can do is:

vector.insert(vector.end(), set.begin(), set.end());

The set's elements are const, so you can't move from them - moving is just copying.

---

After C++17, we get extract():

vector.reserve(set.size());
for (auto it = set.begin(); it != set.end(); ) {
    vector.push_back(std::move(set.extract(it++).value()));
}

Although given your comment that your data is doubles, this wouldn't matter.

来源：https://stackoverflow.com/questions/42519867/efficiently-moving-contents-of-stdunordered-set-to-stdvector