Qt: 网络编程之UDP（理论+实例）

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理论：

    Qt 网络之UDP 网络基础学习是本文要介绍的内容，UDP（User Datagram Protocol即用户数据报协议）是一个轻量级的，不可靠的，面向数据报的无连接协议  。对于UDP我们不再进行过多介绍，如果你对UDP不是很了解，而且不知道它有什么用，那么我们这里就举个简单的例子：我们现在几乎每个人都使用的腾讯QQ，其聊天时就是使用UDP协议进行消息发送的  。就像QQ那样，当有很多用户，发送的大部分都是短消息，要求能及时响应，并且对安全性要求不是很高的情况下使用UDP协议。

　　在Qt中提供了QUdpSocket 类来进行UDP数据报（datagrams）的发送和接收  。这里我们还要了解一个名词Socket，也就是常说的“套接字”  。 Socket简单地说，就是一个IP地址加一个port端口  。因为我们要传输数据，就要知道往哪个机子上传送，而IP地址确定了一台主机，但是这台机子上可能运行着各种各样的网络程序，我们要往哪个程序中发送呢？这时就要使用一个端口来指定UDP程序  。所以说，Socket指明了数据报传输的路径。

实例：

功能：server（图右）端每隔一秒钟，想UDP管道中写入数据，client（图左）端从管道中读出数据，并显示到界面上。

效果图：

服务器端源码：

//weatherballon.h

#ifndef WEATHERBALLON_H#define WEATHERBALLON_H#include <QPushButton>#include <QTimer>#include <QUdpSocket>class WeatherBallon : public QPushButton{    Q_OBJECTpublic:    WeatherBallon(QWidget *parent = 0);    ~WeatherBallon();    double temperature() const;    double humidity() const;    double altitude() const;private slots:    void onSendDatagram();private:    QUdpSocket mUdpSocket;    QTimer timer;};#endif // WEATHERBALLON_H

//weatherballon.cpp

#include <QDateTime>#include <QIODevice>#include <QByteArray>#include "weatherballon.h"WeatherBallon::WeatherBallon(QWidget *parent) : QPushButton (tr("quit"),parent){    connect(this,SIGNAL(clicked(bool)),this,SLOT(close()));    connect(&timer,SIGNAL(timeout()),this,SLOT(onSendDatagram()));    timer.start(1000);    setWindowTitle(tr("Weather Server"));}WeatherBallon::~WeatherBallon(){}double WeatherBallon::temperature() const{    return -20.0 + (2.0 * std::rand() / (RAND_MAX + 1.0));}double WeatherBallon::humidity() const{    return 20.0 + (2.0 * std::rand() / (RAND_MAX + 1.0));}double WeatherBallon::altitude() const{    return 7000 + (100.0 * std::rand() / (RAND_MAX + 1.0));}void WeatherBallon::onSendDatagram(){    QByteArray datagram;    QDataStream out(&datagram, QIODevice::WriteOnly);    out.setVersion(QDataStream::Qt_5_7);    out<<QDateTime::currentDateTime() <<temperature() << humidity() <<altitude();    mUdpSocket.writeDatagram(datagram,QHostAddress::LocalHost ,5824);}

客户端源码：

//weatherstation.h

#ifndef WEATHERSTATION_H#define WEATHERSTATION_H#include <QDialog>#include <QLabel>#include <QLineEdit>#include <QtNetwork/QUdpSocket>class WeatherStation : public QDialog{    Q_OBJECTpublic:    WeatherStation(QWidget *parent = 0);    ~WeatherStation();private slots:    void onProcessPendingDatagrams();private:    QUdpSocket mUdpSocket;    QLabel *mDataLabel;    QLabel *mTimeLabel;    QLabel *mTemperatureLabel;    QLabel *mhumidtyLabel;    QLabel *mAltitudeLabel;    QLineEdit *mDateLineEdit;    QLineEdit *mTimeLineEdit;    QLineEdit *mTemperatureLineEdit;    QLineEdit *mHunidityLineEdit;    QLineEdit *mAltitudeLineEdit;};#endif // WEATHERSTATION_H

//weatherstation.cpp

#include <QGridLayout>#include <QTimer>#include <QDateTime>#include "weatherstation.h"WeatherStation::WeatherStation(QWidget *parent)    : QDialog(parent){    mUdpSocket.bind(5824);    connect(&mUdpSocket,SIGNAL(readyRead()),SLOT(onProcessPendingDatagrams()));    mDataLabel = new QLabel(tr("Data:"));    mTimeLabel = new QLabel(tr("Time:"));    mTemperatureLabel = new QLabel(tr("Temperature:"));    mhumidtyLabel = new QLabel(tr("Hunidity:"));    mAltitudeLabel = new QLabel(tr("Altitude:"));    mDateLineEdit = new QLineEdit;    mTimeLineEdit = new QLineEdit;    mTemperatureLineEdit = new QLineEdit;    mHunidityLineEdit = new QLineEdit;    mAltitudeLineEdit = new QLineEdit;    mDateLineEdit->setReadOnly(true);    mTimeLineEdit->setReadOnly(true);    mTemperatureLineEdit->setReadOnly(true);    mHunidityLineEdit->setReadOnly(true);    mAltitudeLineEdit->setReadOnly(true);    QGridLayout *mainLayout = new QGridLayout;    mainLayout->addWidget(mDataLabel,0,0);    mainLayout->addWidget(mDateLineEdit,0,1);    mainLayout->addWidget(mTimeLabel,1,0);    mainLayout->addWidget(mTimeLineEdit,1,1);    mainLayout->addWidget(mTemperatureLabel,2,0);    mainLayout->addWidget(mTemperatureLineEdit,2,1);    mainLayout->addWidget(mhumidtyLabel,3,0);    mainLayout->addWidget(mHunidityLineEdit,3,1);    mainLayout->addWidget(mAltitudeLabel,4,0);    mainLayout->addWidget(mAltitudeLineEdit,4,1);    setLayout(mainLayout);    setWindowTitle(tr("Weather Station"));}WeatherStation::~WeatherStation(){}void WeatherStation::onProcessPendingDatagrams(){    QByteArray datagram;    while(mUdpSocket.hasPendingDatagrams()) //是否有数据包等待读取    {        datagram.resize(mUdpSocket.pendingDatagramSize()); //        mUdpSocket.readDatagram(datagram.data(), datagram.size());    }    QDateTime dateTime;    double temperature;    double humidity;    double altitude;    QDataStream in(&datagram,QIODevice::ReadOnly); //从datagram中读取数据    in.setVersion(QDataStream::Qt_5_7);    in>>dateTime >> temperature >>humidity >>altitude;    mDateLineEdit->setText(dateTime.date().toString());    mTimeLineEdit->setText(dateTime.time().toString());    mTemperatureLineEdit->setText(tr("%1 C").arg(temperature));    mHunidityLineEdit->setText(tr("%1%").arg(humidity));    mAltitudeLineEdit->setText(tr("%1 m").arg(altitude));}