容器适配器(一):queue

除了标准的顺序容器外，STL还提供了3种容器适配器，queue,priority_queue和stack

适配器是对顺序容器的包装，它的作用是简化接口.

queue接口十分的简单，只有8个方法。再加上构造函数和比较运算符，push()和emplace()

在queue末尾添加元素。Pop()从头部移除元素。通过front()和back()可以返回头部和尾部元素的引用；切记：pop()不会返回一个元素的副本，如果需要这个pop()的元素，这在之前调用front()方法；

在PacketBuffer.h文件里：

#ifndef QUEUE_PACKETBUFFER_H
#define QUEUE_PACKETBUFFER_H

#include <queue>
template<typename T>
class PacketBuffer
{
public:
    PacketBuffer(int maxSize = 0);
    bool packetBuffer(const T& packet);
    T getNextPacket();

private:
    std::queue<T> mPackets;
    int mMaxSize;
};


#endif //QUEUE_PACKETBUFFER_H

在PacketBuffer.cpp文件里：

//
// Created by Administrator on 2019/2/18.
//

#include <stdexcept>
#include "PacketBuffer.h"

template<typename T>
PacketBuffer<T>::PacketBuffer(int maxSize)
:mMaxSize(maxSize)
{

}
template<typename T>
bool PacketBuffer<T>::packetBuffer(const T& packet)
{
    if(mMaxSize > 0 && mPackets.size() == mMaxSize)
    {
        return false;
    }
    mPackets.push(packet);
    return true;
}
template<typename T>
T PacketBuffer<T>::getNextPacket()
{
    if(mPackets.empty())
    {
        throw std::out_of_range("packet is empty
");
    }
    T temp = mPackets.front();
    mPackets.pop();
    return temp;
}

在main里：

#include <iostream>
#include "PacketBuffer.h"
#include "PacketBuffer.cpp"
class IPPacket
{
public:
    IPPacket(int id)
    :mId(id)
    {

    }
    int getId()
    {
        return mId;
    }

private:
    int mId;
};

int main()
{
    PacketBuffer<IPPacket> packet(3);
    for(int i = 1;i <= 4;++i)
    {
        if(!packet.packetBuffer(IPPacket(i)))
        {
            std::cout << "Packet " << i << " dropped (queue is full)" << std::endl;
        }

    }
    while(true)
    {

        try
        {
            IPPacket ipage = packet.getNextPacket();
            std::cout << "id :" << ipage.getId() << std::endl;

        }catch (const std::out_of_range&)
        {
            std::cout << "out of range!" << std::endl;
            break;
        }
    }
    return 0;
}

结果是：

Packet 4 dropped (queue is full)
id :1
id :2
id :3
out of range!