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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); boTargetIP->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(){quint16port = 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 (boTargetIP->findText(IP) < 0)boTargetIP->addItem(IP); } } }}void QGuiUdpClient::actClear_triggered(){ui.plainTextEdit->clear();}void QGuiUdpClient::btnSend_clicked(){QStringtargetIP = boTargetIP->currentText(); //目标IP QHostAddress targetAddr(targetIP); quint16targetPort = 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(){quint16targetPort = 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); boTargetIP->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(){quint16port = 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 (boTargetIP->findText(IP) < 0)boTargetIP->addItem(IP); } } }}void QGuiUdpServer::actClear_triggered(){ui.plainTextEdit->clear();}void QGuiUdpServer::btnSend_clicked(){QStringtargetIP = boTargetIP->currentText(); //目标IP QHostAddress targetAddr(targetIP); quint16targetPort = 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(){quint16targetPort = 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;}
