循環隊列是一種具有固定大小的隊列，當隊列滿時，新元素將會覆蓋最舊的元素。下面是一個簡單的C++循環隊列的應用實例，實現了一個基本的生產者-消費者模型。

#include <iostream>
using namespace std;

#define SIZE 5

class CircularQueue {
private:
    int arr[SIZE];
    int front, rear;

public:
    CircularQueue() {
        front = -1;
        rear = -1;
    }

    void enqueue(int value) {
        if ((front == 0 && rear == SIZE - 1) || (rear == (front - 1) % (SIZE - 1))) {
            cout << "Queue is full" << endl;
        } else if (front == -1) {
            front = rear = 0;
            arr[rear] = value;
        } else if (rear == SIZE - 1 && front != 0) {
            rear = 0;
            arr[rear] = value;
        } else {
            rear++;
            arr[rear] = value;
        }
    }

    int dequeue() {
        if (front == -1) {
            cout << "Queue is empty" << endl;
            return -1;
        }

        int value = arr[front];
        arr[front] = -1;
        if (front == rear) {
            front = rear = -1;
        } else if (front == SIZE - 1) {
            front = 0;
        } else {
            front++;
        }

        return value;
    }

    void displayQueue() {
        if (front == -1) {
            cout << "Queue is empty" << endl;
            return;
        }

        cout << "Elements in the circular queue are:" << endl;
        if (rear >= front) {
            for (int i = front; i <= rear; i++) {
                cout << arr[i] << " ";
            }
        } else {
            for (int i = front; i < SIZE; i++) {
                cout << arr[i] << " ";
            }

            for (int i = 0; i <= rear; i++) {
                cout << arr[i] << " ";
            }
        }
        cout << endl;
    }
};

int main() {
    CircularQueue q;

    q.enqueue(1);
    q.enqueue(2);
    q.enqueue(3);
    q.enqueue(4);
    q.enqueue(5);

    q.displayQueue();

    cout << "Dequeued element: " << q.dequeue() << endl;

    q.enqueue(6);
    q.displayQueue();

    return 0;
}

在這個示例中，我們定義了一個CircularQueue類，實現了循環隊列的基本功能，包括入隊、出隊和顯示隊列元素。在main函數中，我們演示了如何使用循環隊列模擬生產者-消費者模型。首先入隊5個元素，然后出隊一個元素，最后再入隊一個元素。最終打印出隊列中的元素。