Learn Container Adaptors: stack, queue, priority_queue

Definition

Container adaptors in C++ are wrappers that provide a simplified, restricted interface to existing container types.

Unlike sequence or associative containers, adaptors like std::stack, std::queue, and std::priority_queue hide iterators and limit element access. They model specific data structures, offering clear and focused operations such as push, pop, and top/front access.

Stacks (LIFO);
Queues (FIFO);
Priority queues (heap-based).

Adaptors achieve this by wrapping an existing container such as std::deque, std::vector, or std::list and forwarding operations while constraining access. You typically use a container adaptor when you need a strict stack, queue, or priority queue abstraction and do not require direct access to elements or iteration.

main.cpp


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#include <iostream>
#include <stack>
#include <queue>

int main()
{
    std::stack<int> s;
    s.push(10);
    s.push(20);
    std::cout << "Stack top: " << s.top() << "\n";
    
    s.pop();
    std::cout << "Stack top after pop: " << s.top() << "\n";
}

The std::priority_queue adaptor provides a way to maintain a collection of elements in heap order, so that the largest (by default) element is always accessible at the top. Internally, it uses a random-access container such as std::vector and maintains the heap invariant using algorithms like std::push_heap and std::pop_heap.

You should use std::priority_queue when you need fast access to the highest-priority element and efficient insertion and removal, but do not require iteration or random access to other elements. It is ideal for scheduling, event simulation, and any scenario involving dynamic sets where priority-based retrieval is crucial.

main.cpp


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#include <iostream>
#include <queue>
#include <vector>
#include <string>

struct Task {
    int priority;
    std::string description;
    // Higher priority comes first
    bool operator<(const Task& other) const { return priority < other.priority; }
};

int main()
{
    std::priority_queue<Task> tasks;
    tasks.push({3, "Write report"});
    tasks.push({1, "Check email"});
    tasks.push({5, "Fix bug"});

    while (!tasks.empty())
    {
        std::cout << "Next task: " << tasks.top().description << " (priority " << tasks.top().priority << ")\n";
        tasks.pop();
    }
}

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Section 2. Chapter 6

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Definition

Container adaptors in C++ are wrappers that provide a simplified, restricted interface to existing container types.

Stacks (LIFO);
Queues (FIFO);
Priority queues (heap-based).

main.cpp


              1234567891011121314
            
#include <iostream>
#include <stack>
#include <queue>

int main()
{
    std::stack<int> s;
    s.push(10);
    s.push(20);
    std::cout << "Stack top: " << s.top() << "\n";
    
    s.pop();
    std::cout << "Stack top after pop: " << s.top() << "\n";
}

main.cpp


              12345678910111213141516171819202122232425
            
#include <iostream>
#include <queue>
#include <vector>
#include <string>

struct Task {
    int priority;
    std::string description;
    // Higher priority comes first
    bool operator<(const Task& other) const { return priority < other.priority; }
};

int main()
{
    std::priority_queue<Task> tasks;
    tasks.push({3, "Write report"});
    tasks.push({1, "Check email"});
    tasks.push({5, "Fix bug"});

    while (!tasks.empty())
    {
        std::cout << "Next task: " << tasks.top().description << " (priority " << tasks.top().priority << ")\n";
        tasks.pop();
    }
}

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 6