How can I access the underlying container of an STL priority_queue?

Accessing the Underlying Container of STL Container Adaptors

The Standard Template Library (STL) provides container adaptors like stack, queue, and priority_queue, which offer a convenient interface while providing an abstracted layer over the underlying container. However, there is a lack of a standardized method to access the underlying container in these adaptors.

Current Implementation

In some implementations of the STL, such as Microsoft's Visual Studio 2008, a non-standard method called _Get_container() is available for stack and queue. However, no such method exists for priority_queue.

Accessing the Underlying Container in priority_queue

Despite the lack of a standard method, a workaround has been devised:

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

This code defines a helper function Container() that utilizes a nested private class HackedQueue to access the underlying container c.

Usage

With this workaround, you can access the underlying container of priority_queue as follows:

<code class="cpp">priority_queue<SomeClass> pq;
vector<SomeClass>& tasks = Container(pq);</code>

Official Documentation

The official documentation for the STL can be found at the following link:

• [C : Standard Template Library](https://en.cppreference.com/w/cpp/container)

Conclusion

While there is no standard method to access the underlying container of STL container adaptors, the workaround provided offers a solution for priority_queue specifically. For stack and queue, the non-standard _Get_container() method can be utilized if available.

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