How to Access the Underlying Containers in STL Container Adaptors?

Accessing Underlying Containers in STL Container Adaptors

In C , STL container adaptors layer additional functionality over existing containers. However, accessing the underlying container in these adaptors may be desirable for certain operations.

Method for Stack and Queue

For stack and queue, there is a non-standard method called _Get_container() that can retrieve the underlying container. However, this method is not part of the standard and its availability may vary across implementations.

Method for Priority_queue

Unfortunately, there is no standard method to access the underlying container of a priority_queue.

Alternative Approach

One alternative approach for all three container adaptors is to use a privately derived class with access to the underlying container. For example, for a priority_queue:

<code class="cpp">template <class T, class S, class C>
S&amp; Container(priority_queue<T, S, C>&amp; q) {
    struct HackedQueue : private priority_queue<T, S, C> {
        static S&amp; Container(priority_queue<T, S, C>&amp; q) {
            return q.*&amp;HackedQueue::c;
        }
    };
    return HackedQueue::Container(q);
}</code>

This approach allows access to the underlying container through the Container() function.

Standard Library Documentation

Official documentation for the C standard library can be found at the following locations:

• [C Reference](https://en.cppreference.com/w/)
• [STL Tutorial](https://www.learncpp.com/cpp-tutorial/the-c-standard-library-48-stl/)

Clarification

The user's goal is to print the contents of a one-value container using a generic function. This can be achieved by accessing the underlying container, which contains the actual data.

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