Reversing a vector with a iterator

[Jack816]

I'm having trouble reversing my vector with iterators. I think the issue might be with me decrementing limit2, but I can't figure it out.
Here is the function call

reverse(vec2.begin(), vec2.end(), vec2.end());

Here is the definition

template<typename Iter>
void reverse(Iter first, Iter limit, Iter limit2)
{

  while (limit != first)
  {
    *first = *limit2;
    ++first;
    --limit2;
  }
}

[keineahnung]

vec2.end() doesn't return a pointer/iterator to the last element of vec2, but rather a pointer to 'one-past-the-end'. So trying to dereference that and assign it to *first is already going to cause major headaches.

[Jack816]

Thanks. I decremented limit2 before the loop and that somewhat solved my problem. It assigns the first three elements correctly, but then incorrectly assigns the last two.
For example std::vector<int> vec1 = {1, 2, 3, 4, 5}; would have the values 5 , 4, 3, 4, 5 after going through reverse.

[keineahnung]

Say you've got a vector of ints: 4, 8, 12, 16, 20, 24

first points to 4
limit2 points to 24

Copy 24 to slot #0 (overwriting 4)
Copy 20 to slot #1 (overwriting 8)
Copy 16 to slot #2 (overwriting 12)
Copy 12 ...

D'oh! You see 12 no longer exists - slot #2 now holds the value 16.
The problem is your source and destination are the same object.
Create a new vector at the top of the function and use that as your destination, maybe, keeping the original intact.

[jlb]

Is there a reason you're not using std::reverse? Have you looked at the code for std::reverse to see how it works? You need to swap the values, not just "replace" them.

http://www.cplusplus.com/reference/algorithm/reverse/
http://www.cplusplus.com/reference/algorithm/iter_swap/