Why use iterators instead of array indices?

Question

Take the following two lines of code:

for (int i = 0; i < some_vector.size(); i++)
{
    //do stuff
}

And this:

for (som         


        

Answer 1

If you have access to C++11 features, then you can also use a range-based for loop for iterating over your vector (or any other container) as follows:

for (auto &item : some_vector)
{
     //do stuff
}

The benefit of this loop is that you can access elements of the vector directly via the item variable, without running the risk of messing up an index or making a making a mistake when dereferencing an iterator. In addition, the placeholder auto prevents you from having to repeat the type of the container elements, which brings you even closer to a container-independent solution.

Notes:

• If you need the the element index in your loop and the operator[] exists for your container (and is fast enough for you), then better go for your first way.
• A range-based for loop cannot be used to add/delete elements into/from a container. If you want to do that, then better stick to the solution given by Brian Matthews.
• If you don't want to change the elements in your container, then you should use the keyword const as follows: for (auto const &item : some_vector) { ... }.