How to correctly implement custom iterators and const_iterators?

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.

• 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.

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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  class MyIterator {
    // iterator class definition goes here
};

typedef MyIterator iterator_type;
typedef MyIterator 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.

Stack Overflow Q#3582608, score: 184