Question

I am trying to efficiently make a copy of a vector. I see two possible approaches:

std::vector<int> copyVecFast1(const std::vector<int>& original) {   std::vector<int> newVec;   newVec.reserve(original.size());   std::copy(original.begin(), original.end(), std::back_inserter(newVec));   return newVec; }  std::vector<int> copyVecFast2(std::vector<int>& original) {   std::vector<int> newVec;   newVec.swap(original);   return newVec; } 

Which of these is preferred, and why? I am looking for the most efficient solution that will avoid unnecessary copying.

Answer 1

Your second example does not work if you send the argument by reference. Did you mean

void copyVecFast(vec<int> original) // no reference {    vector<int> new_;   new_.swap(original);  } 

That would work, but an easier way is

vector<int> new_(original);