How to increment an iterator by 2?

Question

Can anybody tell me how to increment the iterator by 2?

iter++ is available - do I have to do iter+2? How can I achieve this?

Answer 1

std::advance( iter, 2 );

This method will work for iterators that are not random-access iterators but it can still be specialized by the implementation to be no less efficient than iter += 2 when used with random-access iterators.

Answer 2

If you don't know wether you have enough next elements in your container or not, you need to check against the end of your container between each increment. Neither ++ nor std::advance will do it for you.

if( ++iter == collection.end())
  ... // stop

if( ++iter == collection.end())
  ... // stop

You may even roll your own bound-secure advance function.

If you are sure that you will not go past the end, then std::advance( iter, 2 ) is the best solution.