点击上方“Qt学视觉”，选择“星标”公众号重磅干货，第一时间送达

想要学习的同学们还请认真阅读每篇文章，相信你一定会有所收获

UDP通信概述

UDP(UserDatagramProtocol，用户数据报协议)是轻量的、不可靠的、面向数据报(datagram)、无连接的协议，它可以用于对可靠性要求不高的场合与TCP通信不同，两个程序之间进行UDP通信无 需预先建立持久的socket连接，UDP每次发送数据报都需要指定目标地址和端口(如下图所示)。

QUdpSocket类用于实现UDP通信，它从QAbstractSocket类继承，因而与QTcpSocket共享 大部分的接口函数。主要区别是QUdpSocket以数据报传输数据，而不是以连续的数据流。发送数 据报使用函数QUdpSocket::writeDatagram()，数据报的长度一般少于512字节，每个数据报包含发 送者和接收者的IP地址和端口等信息。

要进行UDP数据接收，要用QUdpSocket::bind()函数先绑定一个端口，用于接收传入的数据 报。当有数据报传入时会发射readyRead()信号，使用readDatagram()函数来读取接收到的数据报。UDP消息传送有单播、广播、组播三种模式

• 单播(unicast)模式：一个UDP客户端发出的数据报只发送到另一个指定地址和端口的 UDP客户端，是一对一的数据传输。

• 广播(broadcast)模式：一个UDP客户端发出的数据报，在同一网络范围内其他所有的UDP客户端都可以收到。QUdpSocket支持IPv4广播。广播经常用于实现网络发现的协议。要获取广播数据只需在数据报中指定接收端地址为QHostAddres::Broadcast, —般的广播 地址是 255.255.255.255。

• 组播(multicast)模式：也称为多播。UDP客户端加入到另一个组播IP地址指定的多播 组，成员向组播地址发送的数据报组内成员都可以接收到，类似于QQ群的功能. QUdpSocket::joinMulticastGroup()函数实现加入多播组的功能，加入多播组后，UDP数据 的收发与正常的UDP数据收发方法一样。

使用广播和多播模式，UDP可以实现一些比较灵活的通信功能，而TCP通信只有单播模式， 没有广播和多播模式。所以，UDP通信虽然不能保证数据传输的准确性，但是具有灵活性，一般 的即时通信软件都是基于UDP通信的。

QUdpSocket类从QAbstractSocket继承而来，但是又定义了较多新的功能函数用于实现UDP 特有的一些功能，如数据报读写和多播通信功能。QUdpSocket没有定义新的信号。QUdpSocket 的主要功能函数见表

• bool bind(quint 16 port = 0)

  • 为UDP通信绑定一个端口

• qint64 writeDatagram(QByteArray &datagram, QHostAddress &host, quint 16 port)

  • 向目标地址和端口的UDP客户端发送数据报，返回成功 发送的字节数

• bool hasPendingDatagrams()

  • 当至少有一个数据报需要读取时，返回true

• qint64 pendingDatagramSize()

  • 返回第一个待读取的数据报的大小

• qint64 readDatagram(char *data, qint64 maxSize)

  • 读取一个数据报，返回成功读取的数据报的字节数

• bool joinMulticastGroup(QHostAddress &groupAddress)

  • 加入一个多播组

• bool leaveMulticastGroup(QHostAddress &groupAddress)

  • 离开一个多播组

在单播、广播和多播模式下，UDP程序都是对等的，不像TCP通信那样分为客户端和服务器 端。多播和广播的实现方式基本相同，只是数据报的目标IP地址设置不同，多播模式需要加入多 播组，实现方式有较大差异。

例程如下

头文件

#pragma once#include #include "ui_QGuiUdpClient.h"#include #include class QGuiUdpClient : public QMainWindow{    Q_OBJECTpublic:    QGuiUdpClient(QWidget *parent = Q_NULLPTR);    ~QGuiUdpClient();private slots:    //自定义槽函数    void onSocketStateChange(QAbstractSocket::SocketState socketState);    void onSocketReadyRead();//读取socket传入的数据    void actStart_triggered();    void actStop_triggered();    void actHostInfo_triggered();    void actClear_triggered();    void btnSend_clicked();    void btnBroadcast_clicked();private:    Ui::QGuiUdpClient ui;private:    QLabel* m_pLabSocketState;//socket状态显示标签    QUdpSocket* m_pUdpSocket;//    QString getLocalIP();//获取本机IP地址};

源文件

#include "QGuiUdpClient.h"#include #pragma execution_character_set("utf-8")QGuiUdpClient::QGuiUdpClient(QWidget *parent)    : QMainWindow(parent){    ui.setupUi(this);    m_pLabSocketState = new QLabel("Socket状态：");//    m_pLabSocketState->setMinimumWidth(200);    ui.statusBar->addWidget(m_pLabSocketState);    QString localIP = getLocalIP();//本机IP    this->setWindowTitle(this->windowTitle() + "----本机IP：" + localIP);    ui.comboTargetIP->addItem(localIP);    m_pUdpSocket = new QUdpSocket(this);//用于与连接的客户端通讯的QTcpSocket    connect(m_pUdpSocket, SIGNAL(stateChanged(QAbstractSocket::SocketState)),        this, SLOT(onSocketStateChange(QAbstractSocket::SocketState)));    onSocketStateChange(m_pUdpSocket->state());    connect(m_pUdpSocket, SIGNAL(readyRead()), this, SLOT(onSocketReadyRead()));    connect(ui.actStart, SIGNAL(triggered()), this, SLOT(actStart_triggered()));    connect(ui.actStop, SIGNAL(triggered()), this, SLOT(actStop_triggered()));    connect(ui.actHostInfo, SIGNAL(triggered()), this, SLOT(actHostInfo_triggered()));    connect(ui.actClear, SIGNAL(triggered()), this, SLOT(actClear_triggered()));    connect(ui.btnSend, SIGNAL(clicked()), this, SLOT(btnSend_clicked()));    connect(ui.btnBroadcast, SIGNAL(clicked()), this, SLOT(btnBroadcast_clicked()));}QGuiUdpClient::~QGuiUdpClient(){    m_pUdpSocket->abort();    delete m_pUdpSocket;}void QGuiUdpClient::onSocketStateChange(QAbstractSocket::SocketState socketState){    switch (socketState)    {    case QAbstractSocket::UnconnectedState:        m_pLabSocketState->setText("scoket状态：UnconnectedState");        break;    case QAbstractSocket::HostLookupState:        m_pLabSocketState->setText("scoket状态：HostLookupState");        break;    case QAbstractSocket::ConnectingState:        m_pLabSocketState->setText("scoket状态：ConnectingState");        break;    case QAbstractSocket::ConnectedState:        m_pLabSocketState->setText("scoket状态：ConnectedState");        break;    case QAbstractSocket::BoundState:        m_pLabSocketState->setText("scoket状态：BoundState");        break;    case QAbstractSocket::ClosingState:        m_pLabSocketState->setText("scoket状态：ClosingState");        break;    case QAbstractSocket::ListeningState:        m_pLabSocketState->setText("scoket状态：ListeningState");        break;    }}void QGuiUdpClient::onSocketReadyRead(){    while (m_pUdpSocket->hasPendingDatagrams())    {        QByteArray   datagram;        datagram.resize(m_pUdpSocket->pendingDatagramSize());        QHostAddress    peerAddr;        quint16 peerPort;        m_pUdpSocket->readDatagram(datagram.data(), datagram.size(), &peerAddr, &peerPort);        QString str = datagram.data();        QString peer = "[From " + peerAddr.toString() + ":" + QString::number(peerPort) + "] ";        ui.plainTextEdit->appendPlainText(peer + str);    }}void QGuiUdpClient::actStart_triggered(){    quint16     port = ui.spinBindPort->value(); //本机UDP端口    if (m_pUdpSocket->bind(port))//绑定端口成功    {        ui.plainTextEdit->appendPlainText("**已成功绑定");        ui.plainTextEdit->appendPlainText("**绑定端口：" + QString::number(m_pUdpSocket->localPort()));        ui.actStart->setEnabled(false);        ui.actStop->setEnabled(true);    }    else        ui.plainTextEdit->appendPlainText("**绑定失败");}void QGuiUdpClient::actStop_triggered(){    m_pUdpSocket->abort(); //不能解除绑定    ui.actStart->setEnabled(true);    ui.actStop->setEnabled(false);    ui.plainTextEdit->appendPlainText("**已解除绑定");}void QGuiUdpClient::actHostInfo_triggered(){    QString hostName = QHostInfo::localHostName();//本地主机名    ui.plainTextEdit->appendPlainText("本机主机名：" + hostName + "\n");    QHostInfo   hostInfo = QHostInfo::fromName(hostName);    QList addList = hostInfo.addresses();//    if (!addList.isEmpty())    {        for (int i = 0; i < addList.count(); i++)        {            QHostAddress aHost = addList.at(i);            if (QAbstractSocket::IPv4Protocol == aHost.protocol())            {                QString IP = aHost.toString();                ui.plainTextEdit->appendPlainText("本机IP地址：" + aHost.toString());                if (ui.comboTargetIP->findText(IP) < 0)                    ui.comboTargetIP->addItem(IP);            }        }    }}void QGuiUdpClient::actClear_triggered(){    ui.plainTextEdit->clear();}void QGuiUdpClient::btnSend_clicked(){    QString     targetIP = ui.comboTargetIP->currentText(); //目标IP    QHostAddress    targetAddr(targetIP);    quint16     targetPort = ui.spinTargetPort->value();//目标port    QString  msg = ui.editMsg->text();//发送的消息内容    QByteArray  str = msg.toUtf8();    m_pUdpSocket->writeDatagram(str, targetAddr, targetPort); //发出数据报    ui.plainTextEdit->appendPlainText("[out] " + msg);    ui.editMsg->clear();    ui.editMsg->setFocus();}void QGuiUdpClient::btnBroadcast_clicked(){    quint16     targetPort = ui.spinTargetPort->value(); //目标端口    QString  msg = ui.editMsg->text();    QByteArray  str = msg.toUtf8();    m_pUdpSocket->writeDatagram(str, QHostAddress::Broadcast, targetPort);    ui.plainTextEdit->appendPlainText("[broadcast] " + msg);    ui.editMsg->clear();    ui.editMsg->setFocus();}QString QGuiUdpClient::getLocalIP(){    QString hostName = QHostInfo::localHostName();//本地主机名    QHostInfo   hostInfo = QHostInfo::fromName(hostName);    QString   localIP = "";    QList addList = hostInfo.addresses();//    if (!addList.isEmpty())    {        for (int i = 0; i < addList.count(); i++)        {            QHostAddress aHost = addList.at(i);            if (QAbstractSocket::IPv4Protocol == aHost.protocol())            {                localIP = aHost.toString();                break;            }        }    }    return localIP;}

头文件

#pragma once#include #include "ui_QGuiUdpServer.h"#include #include class QGuiUdpServer : public QMainWindow{    Q_OBJECTpublic:    QGuiUdpServer(QWidget *parent = Q_NULLPTR);    ~QGuiUdpServer();private slots:    //自定义槽函数    void onSocketStateChange(QAbstractSocket::SocketState socketState);    void onSocketReadyRead();//读取socket传入的数据    void actStart_triggered();    void actStop_triggered();    void actHostInfo_triggered();    void actClear_triggered();    void btnSend_clicked();    void btnBroadcast_clicked();private:    Ui::QGuiUdpServer ui;private:    QLabel* m_pLabSocketState;//socket状态显示标签    QUdpSocket* m_pUdpSocket;//    QString getLocalIP();//获取本机IP地址};

源文件

#include "QGuiUdpServer.h"#include #pragma execution_character_set("utf-8")QGuiUdpServer::QGuiUdpServer(QWidget *parent)    : QMainWindow(parent){    ui.setupUi(this);    m_pLabSocketState = new QLabel("Socket状态：");//    m_pLabSocketState->setMinimumWidth(200);    ui.statusBar->addWidget(m_pLabSocketState);    QString localIP = getLocalIP();//本机IP    this->setWindowTitle(this->windowTitle() + "----本机IP：" + localIP);    ui.comboTargetIP->addItem(localIP);    m_pUdpSocket = new QUdpSocket(this);//用于与连接的客户端通讯的QTcpSocket    connect(m_pUdpSocket, SIGNAL(stateChanged(QAbstractSocket::SocketState)),        this, SLOT(onSocketStateChange(QAbstractSocket::SocketState)));    onSocketStateChange(m_pUdpSocket->state());    connect(m_pUdpSocket, SIGNAL(readyRead()), this, SLOT(onSocketReadyRead()));    connect(ui.actStart, SIGNAL(triggered()), this, SLOT(actStart_triggered()));    connect(ui.actStop, SIGNAL(triggered()), this, SLOT(actStop_triggered()));    connect(ui.actHostInfo, SIGNAL(triggered()), this, SLOT(actHostInfo_triggered()));    connect(ui.actClear, SIGNAL(triggered()), this, SLOT(actClear_triggered()));    connect(ui.btnSend, SIGNAL(clicked()), this, SLOT(btnSend_clicked()));    connect(ui.btnBroadcast, SIGNAL(clicked()), this, SLOT(btnBroadcast_clicked()));}QGuiUdpServer::~QGuiUdpServer(){    m_pUdpSocket->abort();    delete m_pUdpSocket;}void QGuiUdpServer::onSocketStateChange(QAbstractSocket::SocketState socketState){    switch (socketState)    {    case QAbstractSocket::UnconnectedState:        m_pLabSocketState->setText("scoket状态：UnconnectedState");        break;    case QAbstractSocket::HostLookupState:        m_pLabSocketState->setText("scoket状态：HostLookupState");        break;    case QAbstractSocket::ConnectingState:        m_pLabSocketState->setText("scoket状态：ConnectingState");        break;    case QAbstractSocket::ConnectedState:        m_pLabSocketState->setText("scoket状态：ConnectedState");        break;    case QAbstractSocket::BoundState:        m_pLabSocketState->setText("scoket状态：BoundState");        break;    case QAbstractSocket::ClosingState:        m_pLabSocketState->setText("scoket状态：ClosingState");        break;    case QAbstractSocket::ListeningState:        m_pLabSocketState->setText("scoket状态：ListeningState");        break;    }}void QGuiUdpServer::onSocketReadyRead(){    while (m_pUdpSocket->hasPendingDatagrams())    {        QByteArray   datagram;        datagram.resize(m_pUdpSocket->pendingDatagramSize());        QHostAddress    peerAddr;        quint16 peerPort;        m_pUdpSocket->readDatagram(datagram.data(), datagram.size(), &peerAddr, &peerPort);        QString str = datagram.data();        QString peer = "[From " + peerAddr.toString() + ":" + QString::number(peerPort) + "] ";        ui.plainTextEdit->appendPlainText(peer + str);    }}void QGuiUdpServer::actStart_triggered(){    quint16     port = ui.spinBindPort->value(); //本机UDP端口    if (m_pUdpSocket->bind(port))//绑定端口成功    {        ui.plainTextEdit->appendPlainText("**已成功绑定");        ui.plainTextEdit->appendPlainText("**绑定端口：" + QString::number(m_pUdpSocket->localPort()));        ui.actStart->setEnabled(false);        ui.actStop->setEnabled(true);    }    else        ui.plainTextEdit->appendPlainText("**绑定失败");}void QGuiUdpServer::actStop_triggered(){    m_pUdpSocket->abort(); //不能解除绑定    ui.actStart->setEnabled(true);    ui.actStop->setEnabled(false);    ui.plainTextEdit->appendPlainText("**已解除绑定");}void QGuiUdpServer::actHostInfo_triggered(){    QString hostName = QHostInfo::localHostName();//本地主机名    ui.plainTextEdit->appendPlainText("本机主机名：" + hostName + "\n");    QHostInfo   hostInfo = QHostInfo::fromName(hostName);    QList addList = hostInfo.addresses();//    if (!addList.isEmpty())    {        for (int i = 0; i < addList.count(); i++)        {            QHostAddress aHost = addList.at(i);            if (QAbstractSocket::IPv4Protocol == aHost.protocol())            {                QString IP = aHost.toString();                ui.plainTextEdit->appendPlainText("本机IP地址：" + aHost.toString());                if (ui.comboTargetIP->findText(IP) < 0)                    ui.comboTargetIP->addItem(IP);            }        }    }}void QGuiUdpServer::actClear_triggered(){    ui.plainTextEdit->clear();}void QGuiUdpServer::btnSend_clicked(){    QString     targetIP = ui.comboTargetIP->currentText(); //目标IP    QHostAddress    targetAddr(targetIP);    quint16     targetPort = ui.spinTargetPort->value();//目标port    QString  msg = ui.editMsg->text();//发送的消息内容    QByteArray  str = msg.toUtf8();    m_pUdpSocket->writeDatagram(str, targetAddr, targetPort); //发出数据报    ui.plainTextEdit->appendPlainText("[out] " + msg);    ui.editMsg->clear();    ui.editMsg->setFocus();}void QGuiUdpServer::btnBroadcast_clicked(){    quint16     targetPort = ui.spinTargetPort->value(); //目标端口    QString  msg = ui.editMsg->text();    QByteArray  str = msg.toUtf8();    m_pUdpSocket->writeDatagram(str, QHostAddress::Broadcast, targetPort);    ui.plainTextEdit->appendPlainText("[broadcast] " + msg);    ui.editMsg->clear();    ui.editMsg->setFocus();}QString QGuiUdpServer::getLocalIP(){    QString hostName = QHostInfo::localHostName();//本地主机名    QHostInfo   hostInfo = QHostInfo::fromName(hostName);    QString   localIP = "";    QList addList = hostInfo.addresses();//    if (!addList.isEmpty())    {        for (int i = 0; i < addList.count(); i++)        {            QHostAddress aHost = addList.at(i);            if (QAbstractSocket::IPv4Protocol == aHost.protocol())            {                localIP = aHost.toString();                break;            }        }    }    return localIP;}