Speed accessing a std::vector by iterator vs by operator[]/index?

Question

Say, I have a

std::vector v;

in my code and I need to access its elements very often in the program, looping them forwa

Answer 1

I had a test yesterday, use [] vs iterator, the code is create a vector with some elements and remove some elements from the vector. This is the code uses operator [] to access elements

  TimeSpent([](){
    std::vector vt = { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 };
    for (int i = int(vt.size()) - 1; i >= 0; i--)
    {
      if (vt[i] % 2 == 0)
      {
        //cout << "removing " << vt[i] << endl;
        vt.erase(vt.begin() + i);
      }
    }
  });

The following code is about access vector elements by using iterator

  TimeSpent([](){
    std::vector vt = { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 };
    for (std::vector::iterator num = vt.begin(); num != vt.end();)
    {
      if (*num % 2 == 0)
      {
        num = vt.erase(num);
      }
      else
      {
        ++num;
      }
    }
  });

Tested by calling them by this function separately

void TimeSpent(std::function func)
{
  const int ONE_MIL = 10000;
  long times = ONE_MIL;
  std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();
  while (times > 0)
  {
    func();
    --times;
  }
  std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
  cout << "time elapsed : " << std::chrono::duration_cast(end - start).count() << endl;
}

Tested environment is visual studio 2013 pro. version 4.5.51650
The results are :
operator[] : 192
iterator : 212
Summary: when we access the vector container, operator [] is faster than iterator.