How to correctly implement custom iterators and const_iterators?
c++, const-iterator, iterator
Solution
- Choose type of iterator which fits your container: input, output, forward etc.
- Use base iterator classes from standard library. For example, `std::iterator` with `random_access_iterator_tag`.These base classes define all type definitions required by STL and do other work.
To avoid code duplication iterator class should be a template class and be parametrized by "value type", "pointer type", "reference type" or all of them (depends on implementation). For example:
// iterator class is parametrized by pointer type
template <typename PointerType> class MyIterator {
// iterator class definition goes here
};
typedef MyIterator<int*> iterator_type;
typedef MyIterator<const int*> const_iterator_type;
Notice `iterator_type` and `const_iterator_type` type definitions: they are types for your non-const and const iterators.
See Also: standard library reference
EDIT: `std::iterator` is deprecated since C++17. See a relating discussion here.
Problem
I have a custom container class for which I'd like to write the `iterator` and `const_iterator` classes. I never did this before and I failed to find an appropriate how-to. What are the guidelines regarding iterator creation, and what should I be aware of ? I'd also like to avoid code duplication (I feel that `const_iterator` and `iterator` share many things; should one subclass the other ?). Foot note: I'm pretty sure Boost has something to ease this but I can't use it here, for many stupid reasons.