在C ++ 14中初始化唯一指针向量的正确方法

Question

For initializing a vector of unique pointers in C++14, I can consider the following two ways. Which method is better?

#include<memory>
#include<vector>
using namespace std;

int main(){

  const int N = 10000000;

  {//first method
    vector<unique_ptr<int>> vec(N);
    for(auto it=vec.begin(); it!=vec.end();++it){
      auto ptr = make_unique<int>();
      *it = std::move(ptr);
    }
  }

  {//second method
    vector<unique_ptr<int>> vec;
    for(int i=0; i<N; i++){
      vec.push_back(make_unique<int>());
    }
  }
}

Answer 1

Either way works. The second is marginally more efficient if you reserve the correct capacity first. Personally, I think the standard algorithms are more expressive. I would do it like this:

std::vector<std::unique_ptr<int>> vec;
vec.reserve(N);
std::generate_n(std::back_inserter(vec), N, [] { return std::make_unique<int>(); });