Intermediate C++ Game Programming Tutorial 15

Iterators are just fancy pointers for containers. In this video we learn how to use iterators, what they're good for, and why we go through all this goddamn trouble in the first place (answer: because they make my dick hard).

Topics Covered

• Iterator operations (increment/decrement, dereference, add/sub, etc.)
• Getting iterators from containers (begin/end)
• Sequence ranges [closed,open)
• Container manipulation functions (erase/insert)
• Iterators and template algorithms (generic algorithms)
• Iterator categories (random access/bidirectional/forward etc.)
• const_iterator (cbegin/cend) & reverse iterators (rbegin/rend)
• Free iterator functions (std::begin/end/advance/next/prev)
• Iterator adapters (back_inserter, ostream_iterator)

Video Timestamp Index

Tutorial 15

• Why should I care about iterators? 0:21
• What are iterators? 0:49
• Valid range for an iterator [first,last) 1:27
• What is the type of an iterator / iterator member type definitions 1:55
• Getting an iterator from a container, using the example std::vector<int>::iterator i = v.begin(); 2:34
• Simple for loops with iterators & iterator arithmetic 3:52
• Code safety through Iterator protection when misused / out of bounds / invalidated 6:48
• Container manipulation function erase 7:20
• Iterators that return iterators (recovering from an invalidation), e.g. i = v.erase(i); 10:17
• Container manipulation function insert / emplace 11:45
• Why not just use indices? Iterators and template algorithms (generic algorithms) 12:36
• Introducing the forward_list container 13:40
• Template a function on an Iterator: writing a generic function that can be applied to any type of container, e.g.
  template<typename Iter>
void print(Iter begin, Iter end){...} 14:35
• Introducing the Algorithms library 15:16
• The five types of iterators: input, output, forward, bidirectional, random access 15:29
• Constant inerators 16:26
• Reverse iterators 17:39
• Free functions and iterators in the Standard library (STL) std::begin(container_object), works on C-arrays so generic Algorithms can be applied 18:22
• Special purpose iterators: Iterator adapters (back_inserter, ostream_iterator) 20:32
• Example code for handling operations on different types of containers, i.e.
  template<typename Iter1, typename Iter2, typename Iter3>
void sum(Iter1 in1, Iter1 end1, Iter2 in2, Iter3 out){...} 20:41
• Example applying a back_insert_iterator on a std::list<float> lf, calling the sum function like so:
  sum( vi.begin(), vi.end(), vf.begin(), std::back_inserter(lf) ) 22:22
• Example code using Stream iterators, e.g. an ostream_iterator, like so:
  sum( vi.begin(), vi.end(), vf.begin(), std::ostream_iterator<float>(std::cout,", ") 23:36
• Homework assignment 24:33

Answer to erase puzzle

The reason why we do not increment the iterator i in the for loop, but instead increment it conditionally in the body of the loop is, if we erase an element, the returned iterator will point to the next element after the erased one, and if we were incrementing every iteration of the loop, it would skip all elements that immediately follow an erased element. Instead, we only increment if we did not erase an element, and this ensures that all elements are tested.

Homework

Modify our linked list stack to work with range based for loops. You are not allowed to modify any code outsize of the Stack class. If you want an extra challenge after completing Level 1, you can uncomment the code for Level 2 and try to get it to compile as well.

Linked List Stack Repo

Solution video

Links

Iterator Category Reference
Custom Iterator Example

See also

• Next in series (Tutorial 16)
• Intermediate C++ Game Programming Series