Should I reserve memory when using std::back_inserter

Question

Do I need to reserve memory when using a back:inserter?

d.reserve(s.size())
std::copy (s.begin(),s.end(),back_inserter(d));

Answer 1

You do not need to reserve memory for the container when using std::back_inserter. However, if you know beforehand about the number of elements you are going to insert and want to prevent repeated allocations you may reserve memory.

Answer 2

You don't have to. However, if this code snippet is run very frequently, you may consider reserving memory to improve performance.