队列（c++实现）

  队列的特点是先进先出，跟栈的c++实现类似，队列的c++实现同样有两种方式：

  Queue是一个接口类，封装了队列相关的所有操作：

//Queue.h
#ifndef __QUEUE_H__
#define __QUEUE_H__

#include <exception>

template<typename T>
class Queue
{
public:
    virtual void add(const T& e) = 0;   //向队列增加元素
    virtual void remove() = 0;          //删除队列(头)元素
    virtual T front() const = 0;        //获取队列(头)元素
    virtual void clear() = 0;           //清空队列
    virtual int length() const = 0;     //获取队列长度
};

#endif /* __QUEUE_H__ */

  队列数据结构其实就是前面讲的环形缓冲区，核心是两个循环计数的指针分别表示读/写位置。
  队列空间是静态分配的数组：

//StaticQueue.h
#ifndef __STATICQUEUE_H__
#define __STATICQUEUE_H__

#include "Queue.h"

template <typename T, int N>
class StaticQueue : public Queue<T>
{
protected:
    T m_space[N];
    int m_write;
    int m_read;
    int m_length;

public:
    StaticQueue() : m_write(0), m_read(0), m_length(0)
    {
    }

    int capacity() const
    {
        return N;
    }

    void add(const T& e)
    {
        if (m_length < N)
        {
            m_space[m_write] = e;
            m_write = (m_write + 1) % N;
            ++m_length;
        }
        else
            throw(std::runtime_error("No space in current queue"));
    }

    void remove()
    {
        if (m_length > 0)
        {
            m_read = (m_read + 1) % N;
            --m_length;
        }
        else
            throw(std::runtime_error("No element in current queue"));
    }

    T front() const
    {
        if (m_length > 0)
            return m_space[m_read];
        else
            throw(std::runtime_error("No element in current queue"));
    }

    void clear()
    {
        m_write = 0;
        m_read = 0;
        m_length = 0;
    }

    int length() const
    {
        return m_length;
    }
};

#endif /* __STATICQUEUE_H__ */

  测试：

//main.cpp
int main(void)
{
    StaticQueue<int, 6> queue;

    for (int i = 0; i < 6; ++i)
    {
        queue.add(i);
    }

    while (queue.length() > 0)
    {
        std::cout << queue.front() << std::endl;
        queue.remove();
    }

    getchar();
    return 0;
}

  用链表实现队列空间，这里采用Linux内核链表来实现：

//LinkQueue.h
#ifndef __LINKQUEUE_H__
#define __LINKQUEUE_H__

#include "linux_list.h"
#include "Queue.h"

template<typename T>
class LinkQueue : public Queue<T>
{
protected:
    struct Node_t
    {
        list_head head;
        T value;
    };

    list_head m_head;
    int m_length;

public:
    LinkQueue()
    {
        m_length = 0;
        INIT_LIST_HEAD(&m_head);
    }

    void add(const T& e)
    {
        Node_t *node = new Node_t();
        if (node)
        {
            node->value = e;
            list_add_tail(&node->head, &m_head);
            ++m_length;
        }
        else
            throw(std::runtime_error("No memory in create queue"));
    }

    void remove()
    {
        if (m_length > 0)
        {
            list_head* toDel = m_head.next;
            list_del(toDel);
            --m_length;
            delete list_entry(toDel, Node_t, head);
        }
        else
            throw(std::runtime_error("No element in current queue"));
    }

    T front() const
    {
        if (m_length > 0)
        {
            return list_entry(m_head.next, Node_t, head)->value;
        }
        else
            throw(std::runtime_error("No element in current queue"));
    }

    void clear()
    {
        while (m_length > 0)
            remove();
    }

    int length() const
    {
        return m_length;
    }

    ~LinkQueue()
    {
        clear();
    }

};

#endif /* __LINKQUEUE_H__ */