C++20 STL Cookbook/

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Create a Random-Access Iterator

Create a Random-Access Iterator

Learn to create a random-access iterator.

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This recipe is an example of a full-featured contiguous iterator, also called a random-access iterator. This is the most complete type of iterator for a container. A random-access iterator includes all the features of all the other types of container iterators, along with its random-access capabilities.

How to do it

We need a container for our iterator. We’ll use a simple array for this, and we’ll call it Container. The iterator class is nested within the Container class.

All of this is designed to be consistent with the STL container interfaces.

  • Container is defined as a template class. Its private section has only two elements:

template<typename T>
class Container {
    std::unique_ptr<T[]> c_{};
    size_t n_elements_{};

We use a unique_pointer for the data. We let the smart pointer manage its own memory. This mitigates the need for a ~Container() destructor. The n_elements_ variable keeps the size of our container.

  • In the public section, we have our constructors:

Container(initializer_list<T> l) : n_elements_{l.size()} {
    c_ = std::make_unique<T[]>(n_elements_);
    size_t index{0};
    for(T e : l) {
        c_[index++] = e;
    }
}

The first constructor uses an initializer_list to pass elements for the container. We call make_unique to allocate space and populate the container with a range-based for ...