C++ Create fixed size queue

Question

In C++, how do you create a simple fixed size queue?

I have done it multiple times in Java and Python but am looking for a C++ based way of doing so.

I need a simple FIFO queue with only 2 elements in order to use the push and pop utilities: I am already aware of the fact that I could implement my own class to perform this kind of restriction but my question aims to know if there exist any already available solution to this.

Or is it maybe possible to accomplish the same task with an array? That would work as well.

Answer 1

You could inherit from queue, and then reimplement the push method. Here is a basic example.

#include <queue>
#include <deque>
#include <iostream>

template <typename T, int MaxLen, typename Container=std::deque<T>>
class FixedQueue : public std::queue<T, Container> {
public:
    void push(const T& value) {
        if (this->size() == MaxLen) {
           this->c.pop_front();
        }
        std::queue<T, Container>::push(value);
    }
};

int main() {
    FixedQueue<int, 3> q;
    q.push(1);
    q.push(2);
    q.push(3);
    q.push(4);
    q.push(5);
    q.push(6);
    q.push(7);

    while (q.size() > 0)
    {
        std::cout << q.front() << std::endl;
        q.pop();
    }
}

This will print

$ g++ fixedqueue.cpp -std=c++17 -o fixedqueue && ./fixedqueue
5
6
7