Std :: vector :: erase vs "swap and pop"

Question

The “normal” way to remove an element from a vector is as follows:

vec.erase(vec.begin() + index); 

But theoretically this is faster, just for this:

 if (vec.size() >= 2) { std::swap(vec.begin() + index, vec.end() - 1); vec.pop_back(); } else { vec.clear(); } 

Is there a reason not to use the latter?

Answer 1

The second case does not preserve the order of elements in the vector. If this is a sorted vector or order is important, then you just violated this in the second case, when the first case left the order intact.