Qt —UDP通信QUdpSocket 简介 +案例

1. UDP通信概述

   UDP是无连接、不可靠、面向数据报（datagram）的协议，可以应用于对可靠性要求不高的场合。与TCP通信不同，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。

   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。
     UDP数据接收，首先要使用QUdpSocket::bind()绑定一个端口，绑定端口后，socket的状态会变为已绑定状态“BoundState”。

当有数据报传入时，QudpSocket会自动发射readyRead()信号，在其槽函数中使用QUdpSocket::readDatagram()进行数据读取。abort()为解除绑定，解除后socket状态变为未连接状态“UnconnectedState”。

2. UDP消息传送的三种模式

单播模式（unicast）：一个UDP客户端发送数据报到指定地址和端口的另一UDP客户端，是一对一的数据传输。

广播模式（broadcast）：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。需要在数据报中指定接收端地址为QHostAddress::Broadcast，一般的广播地址是255.255.255.255。

组播模式（multicast）：UDP客户端加入到另一个组播IP地址的多播组，成员向组播地址发送的数据报，其加入组播的所有成员都可以接收到，类似于QQ群功能。QUdpSocket::joinMulticastGroup()函数实现加入多播组的功能。

QUdpSocket::leaveMulticastGroup()函数实现

在单播、广播和多播模式下，UDP程序都是对等的，不像TCP通信分为客户端和服务端。
TCP通信只有单播模式。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。

3. QUdpSocket类的接口函数

bool bind(quint16 port = 0)  为UDP通信绑定一个端口

qint64 writeDatagram(QByteArray& datagram, QHostAddress& host, quint16 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，数据报的长度一般不超过512字节。

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，返回成功读取的字节数

qint64 readDatagram(char* data, qint64 maxSize, QHostAddress* address, quint16* port) 读取一个数据报，返回成功读取的字节数。发送方的主机地址和端口存储在*address和*port中(除非指针为0)

bool joinMulticastGroup(QHostAddress& groupAddress)      加入一个多播组

bool leaveMulticastGroup(QHostAddress& groupAddress)    离开一个多播组

void abort() 终止当前连接并重置套接字。通常在析构函数中写入。与disconnectFromHost()不同，该函数立即关闭套接字，丢弃写入缓冲区中的任何挂起数据。
原文链接：https://blog.csdn.net/WL0616/article/details/129050373

4.UDP对话小案例

实现发送和接收端互相发信息，类似QQ  (界面使用UI设计)

4.1.接收端

receiver.h

#ifndef RECESIVER_H
#define RECESIVER_H#include <QWidget>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class Recesiver; }
QT_END_NAMESPACEclass Recesiver : public QWidget
{Q_OBJECTpublic:Recesiver(QWidget *parent = nullptr);~Recesiver();private slots:void on_pushButton_2_clicked(); //启动槽函数void start();void on_pushButton_clicked();private:Ui::Recesiver *ui;QUdpSocket *receiver;
};
#endif // RECESIVER_H

receiver.cpp

#include "recesiver.h"
#include "ui_recesiver.h"Recesiver::Recesiver(QWidget *parent): QWidget(parent), ui(new Ui::Recesiver)
{ui->setupUi(this);setWindowTitle(QStringLiteral("接收端"));ui->lineEdit->setText("127.0.0.1");receiver =new QUdpSocket(this);
}Recesiver::~Recesiver()
{delete ui;
}//接收信息void Recesiver::start(){QByteArray datagram;datagram.resize(receiver->pendingDatagramSize()); //接收到的数据的长度receiver->readDatagram(datagram.data(),datagram.size());ui->textEdit->append(QStringLiteral("对方：")+datagram);}//启动按钮（发送端发送信息给接收端）
void Recesiver::on_pushButton_2_clicked()
{receiver->bind(ui->lineEdit_2->text().toInt());//设置端口号将其转为整型connect(receiver,&QUdpSocket::readyRead,this,[&](){start();});ui->pushButton_2->setEnabled(false);ui->lineEdit_2->setEnabled(false);
}//发送按钮（接收端发送信息给发送端）
void Recesiver::on_pushButton_clicked()
{QByteArray datagram=ui->textEdit_2->toPlainText().toUtf8();  //在输入端输入发送的内容receiver->writeDatagram(datagram.data(),datagram.size(),QHostAddress(ui->lineEdit->text()),ui->lineEdit_3->text().toInt());//qint64 writeDatagram(const char *data, qint64 len, const QHostAddress &host, quint16 port);//发送数据，大小，发送主机的ip,发送主机的端口号ui->textEdit->append(QStringLiteral("本机：")+ui->textEdit_2->toPlainText());//发送信息的具体内容在发送端的聊天记录里能体现ui->textEdit_2->clear();
}

4.2发送端

sender.h

#ifndef SENDER_H
#define SENDER_H
#include <QWidget>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class Sender; }
QT_END_NAMESPACEclass Sender : public QWidget
{Q_OBJECTpublic:Sender(QWidget *parent = nullptr);~Sender();void  start2();
private slots:void on_pushButton_clicked();private:Ui::Sender *ui;QUdpSocket *sender;
};
#endif // SENDER_H

sender.cpp

#include "sender.h"
#include "ui_sender.h"Sender::Sender(QWidget *parent): QWidget(parent), ui(new Ui::Sender)
{ui->setupUi(this);sender=new QUdpSocket(this);setWindowTitle(QStringLiteral("发送端"));//senderui->lineEdit_3->setText("888");sender->bind(ui->lineEdit_3->text().toInt());//绑定端口号connect(sender,&QUdpSocket::readyRead,this,[&](){start2();});//start2();
}void Sender::start2()
{QByteArray datagram;datagram.resize(sender->pendingDatagramSize()); //接收到的数据的长度sender->readDatagram(datagram.data(),datagram.size());ui->textEdit->append(QStringLiteral("对方：")+datagram);
}Sender::~Sender()
{delete ui;
}//发送按钮 发送信息给接收端
void Sender::on_pushButton_clicked()
{QByteArray datagram=ui->textEdit_2->toPlainText().toUtf8();  //在输入端输入发送的内容sender->writeDatagram(datagram.data(),datagram.size(),QHostAddress(ui->lineEdit->text()),ui->lineEdit_2->text().toInt());//qint64 writeDatagram(const char *data, qint64 len, const QHostAddress &host, quint16 port);//发送数据，大小，发送主机的ip,发送主机的端口号ui->textEdit->append(QStringLiteral("本机：")+ui->textEdit_2->toPlainText());//发送信息的具体内容在发送端的聊天记录里能体现ui->textEdit_2->clear();}

结果：

（ps：对话有点搞笑，哈哈哈）

5.4. UDP单播和广播代码示例

4.1 测试说明

  本实例实现UDP通信的单播和广播。两个实例可以运行在同一台计算机上，也可以运行在不同的计算机上。
这里的两个实例是运行在同一台计算机上，需要注意，在同一台计算机上运行时，两个实例需要绑定不同的端口。例如实例A绑定端口1600，实例B绑定端口3200，实例A向实例B发送数据报时，需要指定实例B的端口，这样实例B才能收到数据。
如果两个实例在不同的计算机上运行，则端口可以一样，因为IP地址不同了，不会导致绑定时发生冲突。一般的UDP通信程序都是在不同的计算机上运行的，约定一个固定的端口作为通信端口。

4.2主要程序

用UI设计器件和代码化UI分别设计

ui设计器设计：

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QMainWindow>
#include <QLabel>
#include <QAbstractSocket>
#include <QUdpSocket>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACEclass MainWindow : public QMainWindow
{Q_OBJECTpublic:MainWindow(QWidget *parent = nullptr);~MainWindow();void   handleEvents();                                                 // 信号与槽处理private:Ui::MainWindow *ui;QUdpSocket *udpScoket;QLabel *labstateScoket;   //Scoket状态栏标签QString  getLocalIp();  //获取本机的IP地址
private slots:void slotActBindPort();   //绑定端口void slotActUnbindPort(); //解除端口void slotActClearText();  //清空文本框void slotActQuit();       //退出void slotSocketReadyRead();  //读取socket传入的数据void slotSocketStateChanged(QAbstractSocket::SocketState socketState);void on_pushButton_clicked(); //发送信息void on_pushButton_2_clicked(); //广播信息
};
#endif // MAINWINDOW_H

.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QTextEdit>
#include <QMessageBox>
#include <QHostInfo>#include <QAction>
#include <QPushButton>
MainWindow::MainWindow(QWidget *parent): QMainWindow(parent), ui(new Ui::MainWindow)
{ui->setupUi(this);QString localIP = getLocalIp(); //获取本机的IP地址this->setWindowTitle(this->windowTitle() + "---IP:" + localIP);ui->comboBox->addItem(localIP); //在目标地址中添加IPudpScoket = new QUdpSocket(this);//状态栏labstateScoket = new QLabel(QStringLiteral("socket状态："), this);labstateScoket->setMinimumWidth(150);ui->statusBar->addWidget(labstateScoket);handleEvents();ui->spinBox->setMinimum(1);     //设置绑定端口的最大最小值和当前的端口值ui->spinBox->setMaximum(65535);ui->spinBox->setValue(1600);ui->spinBox_2->setMinimum(1);   //设置目标端口的最大最小值和当前的端口值ui->spinBox_2->setMaximum(65535);ui->spinBox_2->setValue(3200);}MainWindow::~MainWindow()
{udpScoket->abort();delete udpScoket;udpScoket = nullptr;delete ui;
}// 信号与槽处理
void MainWindow::handleEvents()
{connect(ui->action, &QAction::triggered, this, &MainWindow::slotActBindPort );connect(ui->action_2, &QAction::triggered, this, &MainWindow::slotActUnbindPort);connect(ui->action_3, &QAction::triggered, this, &MainWindow::slotActClearText);connect(ui->action_4, &QAction::triggered, this, &MainWindow::slotActQuit);connect(ui->pushButton, &QPushButton::clicked, this, &MainWindow::on_pushButton_clicked);connect(ui->pushButton_2, &QPushButton::clicked, this, &MainWindow::on_pushButton_2_clicked);connect(udpScoket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);connect(udpScoket, &QUdpSocket::readyRead, this, &MainWindow::slotSocketReadyRead);}QString MainWindow::getLocalIp()
{QString hostName = QHostInfo::localHostName();//获取本机主机名QHostInfo hostInfo = QHostInfo::fromName(hostName);  //返回主机名的IP地址QString localIP = "";QList<QHostAddress> addrList = hostInfo.addresses();   //主机IP地址列表if (!addrList.isEmpty()){for (int i = 0; i < addrList.size(); i++){QHostAddress addr = addrList.at(i);if (QAbstractSocket::IPv4Protocol == addr.protocol()){localIP = addr.toString();break;}}}return localIP;
}//绑定端口
void MainWindow::slotActBindPort()
{quint16 port=ui->spinBox->value();   //绑定本机UDp端口if(udpScoket->bind(port)){ui->textEdit->append(QStringLiteral("**已经绑定成功"));ui->textEdit->append(QStringLiteral("**绑定端口：")+QString::number(udpScoket->localPort()));ui->action->setEnabled(false); //开始绑定失效ui->action_2->setEnabled(true);//解除绑定使能}elseui->textEdit->append(QStringLiteral("绑定失败"));
}//解除端口
void MainWindow::slotActUnbindPort()
{udpScoket->abort();//解除绑定ui->action->setEnabled(true); //开始绑定失效ui->action_2->setEnabled(false);//解除绑定使能ui->textEdit->append(QStringLiteral("**已经解除绑定"));}//清空文本框
void MainWindow::slotActClearText()
{ui->textEdit->clear();
}//退出
void MainWindow::slotActQuit()
{QMessageBox::StandardButton button = QMessageBox::question(this, "", QStringLiteral("是否要退出？"));if (button == QMessageBox::StandardButton::Yes)this->close();
}//读取socket传入的数据
void MainWindow::slotSocketReadyRead()
{while(udpScoket->hasPendingDatagrams()) //当有数据传入数据报{QByteArray  datagtam;datagtam.resize(udpScoket->pendingDatagramSize());//读取数据报大小QHostAddress peerAddr;  //在已连接的状态下，返回对方的socket的地址quint16 peerPort;       //在已连接的状态下，返回对方的socket的端口udpScoket->readDatagram(datagtam.data(),datagtam.size(),&peerAddr,&peerPort);//读取数据报的内容//qint64 readDatagram(char *data, qint64 maxlen, QHostAddress *host = nullptr, quint16 *port = nullptr);QString str=datagtam.data();QString  peer="[From "+peerAddr.toString()+":"+QString::number(peerPort)+"]";ui->textEdit->append( peer + str);}
}//状态栏显示Socket变化情况
void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState)
{switch (socketState){case QAbstractSocket::UnconnectedState: labstateScoket->setText(QStringLiteral("socket状态：UnconnectedState")); break;case QAbstractSocket::HostLookupState: labstateScoket->setText(QStringLiteral("socket状态：HostLookupState")); break;case QAbstractSocket::ConnectingState: labstateScoket->setText(QStringLiteral("socket状态：ConnectingState")); break;case QAbstractSocket::ConnectedState: labstateScoket->setText(QStringLiteral("socket状态：ConnectedState")); break;case QAbstractSocket::BoundState: labstateScoket->setText(QStringLiteral("socket状态：BoundState")); break;case QAbstractSocket::ClosingState: labstateScoket->setText(QStringLiteral("socket状态：ClosingState")); break;default: break;}}//发送信息
void MainWindow::on_pushButton_clicked()
{QString msg = ui->lineEdit->text(); //发送信息QByteArray str = msg.toUtf8();QString targetIp = ui->comboBox->currentText();  //目标IP就是主机地址的ipQHostAddress targetAddr(targetIp);quint16 targetPort = ui->spinBox_2->value();  //目标端口udpScoket->writeDatagram(str, targetAddr, targetPort);//发出数据报ui->textEdit->append("[out] " + msg);ui->lineEdit->clear();ui->lineEdit->setFocus();}
//广播信息
void MainWindow::on_pushButton_2_clicked()
{quint16 targetPort = ui->spinBox_2->value();  //目标端口QString msg=ui->lineEdit->text();QByteArray str = msg.toUtf8();udpScoket->writeDatagram(str, QHostAddress::Broadcast, targetPort);//发出数据报ui->textEdit->append("[broadcast] " + msg);ui->lineEdit->clear();ui->lineEdit->setFocus();}

代码化：

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QAction>
#include <QComboBox>
#include <QGridLayout>
#include <QHBoxLayout>
#include <QHostInfo>
#include <QLabel>
#include <QLineEdit>
#include <QMainWindow>
#include <QMessageBox>
#include <QPlainTextEdit>
#include <QPushButton>
#include <QSpinBox>
#include <QUdpSocket>
#include <QVBoxLayout>namespace Ui {class MainWindow;
}class MainWindow : public QMainWindow {Q_OBJECTpublic:explicit MainWindow(QWidget* parent = 0);~MainWindow();private slots:void slotActBindPort();void slotActUnbindPort();void slotActClearText();void slotActQuit();void slotSocketStateChanged(QAbstractSocket::SocketState socketState);void slotBtnSend();void slotBtnBroad();void slotSocketReadyRead();  //读取socket传入的数据private:Ui::MainWindow* ui;QAction* m_pActBindPort;QAction* m_pActUnbindPort;QAction* m_pActClearText;QAction* m_pActQuit;QWidget* m_pCentralWidget;QLabel* m_pLabBindPort;QLabel* m_PLabTargetAddr;QLabel* m_pLabTargetPort;QSpinBox* m_pSpinBindPort;QComboBox* m_pComboTargetAddr;QSpinBox* m_pSpinTargetPort;QLineEdit* m_pLineEdit;QPushButton* m_pBtnSend;QPushButton* m_pBtnBroad;QPlainTextEdit* m_pPlainText;QLabel* m_pLabState;QUdpSocket* m_pUdpSocket;QString getLocalIP();
};#endif  // MAINWINDOW_H

.cpp

#include "mainwindow.h"
#include <QToolBar>
#include "ui_mainwindow.h"MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent), ui(new Ui::MainWindow) {ui->setupUi(this);//this->setWindowIcon(QIcon(":/new/prefix1/res/TitleIcon.png"));this->setWindowTitle(QStringLiteral("UDP Send/Receiver"));//工具栏ui->toolBar->setToolButtonStyle(Qt::ToolButtonTextBesideIcon);m_pActBindPort = new QAction(QIcon(":/new/Check.png"), QStringLiteral("绑定端口"), this);m_pActUnbindPort = new QAction(QIcon(":/new/Break.png"), QStringLiteral("结束绑定"), this);m_pActClearText = new QAction(QIcon(":/new/remove.png"), QStringLiteral("清空文本"), this);m_pActQuit = new QAction(QIcon(":/new/back.png"), QStringLiteral("退出"), this);ui->toolBar->addAction(m_pActBindPort);ui->toolBar->addAction(m_pActUnbindPort);ui->toolBar->addSeparator();ui->toolBar->addAction(m_pActClearText);ui->toolBar->addSeparator();ui->toolBar->addAction(m_pActQuit);//界面布局m_pCentralWidget = new QWidget(this);QHBoxLayout* HLay1 = new QHBoxLayout;m_pLabBindPort = new QLabel(QStringLiteral("绑定端口"), m_pCentralWidget);m_pSpinBindPort = new QSpinBox(m_pCentralWidget);m_pSpinBindPort->setMinimum(1);m_pSpinBindPort->setMaximum(65535);m_pSpinBindPort->setValue(3200);m_PLabTargetAddr = new QLabel(QStringLiteral("目标地址"), m_pCentralWidget);m_pComboTargetAddr = new QComboBox(m_pCentralWidget);m_pLabTargetPort = new QLabel(QStringLiteral("目标端口"), m_pCentralWidget);m_pSpinTargetPort = new QSpinBox(m_pCentralWidget);m_pSpinTargetPort->setMinimum(1);m_pSpinTargetPort->setMaximum(65535);m_pSpinTargetPort->setValue(1600);HLay1->addWidget(m_pLabBindPort, 1, Qt::AlignRight);HLay1->addWidget(m_pSpinBindPort, 2);HLay1->addWidget(m_PLabTargetAddr, 1, Qt::AlignRight);HLay1->addWidget(m_pComboTargetAddr, 4);HLay1->addWidget(m_pLabTargetPort, 1, Qt::AlignRight);HLay1->addWidget(m_pSpinTargetPort, 2);QHBoxLayout* HLay2 = new QHBoxLayout;m_pLineEdit = new QLineEdit(m_pCentralWidget);m_pBtnSend = new QPushButton(QStringLiteral("发送消息"), m_pCentralWidget);m_pBtnBroad = new QPushButton(QStringLiteral("广播消息"), m_pCentralWidget);HLay2->addWidget(m_pLineEdit);HLay2->addWidget(m_pBtnSend);HLay2->addWidget(m_pBtnBroad);QVBoxLayout* VLay = new QVBoxLayout(m_pCentralWidget);  //主布局必须设置parent，否则不会显示布局// QVBoxLayout* VLay = new QVBoxLayout();VLay->addLayout(HLay1);VLay->addLayout(HLay2);m_pPlainText = new QPlainTextEdit(m_pCentralWidget);VLay->addWidget(m_pPlainText);this->setCentralWidget(m_pCentralWidget);this->setLayout(VLay);  //设置为窗体的主布。在指定了主布局的parent之后，这句话可有可无QString localIP = getLocalIP();this->setWindowTitle(this->windowTitle() + "---IP:" + localIP);m_pComboTargetAddr->addItem(localIP);m_pUdpSocket = new QUdpSocket(this);//状态栏m_pLabState = new QLabel(QStringLiteral("socket状态："), this);m_pLabState->setMinimumWidth(150);ui->statusbar->addWidget(m_pLabState);// connectconnect(m_pActBindPort, &QAction::triggered, this, &MainWindow::slotActBindPort);connect(m_pActUnbindPort, &QAction::triggered, this, &MainWindow::slotActUnbindPort);connect(m_pActClearText, &QAction::triggered, this, &MainWindow::slotActClearText);connect(m_pActQuit, &QAction::triggered, this, &MainWindow::slotActQuit);connect(m_pBtnSend, &QPushButton::clicked, this, &MainWindow::slotBtnSend);connect(m_pBtnBroad, &QPushButton::clicked, this, &MainWindow::slotBtnBroad);connect(m_pUdpSocket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);connect(m_pUdpSocket, &QUdpSocket::readyRead, this, &MainWindow::slotSocketReadyRead);
}MainWindow::~MainWindow() {//m_pUdpSocket->abort();//delete m_pUdpSocket;//m_pUdpSocket = nullptr;delete ui;
}void MainWindow::slotActBindPort()
{quint16 port = m_pSpinBindPort->value();  //本机UDP端口if (m_pUdpSocket->bind(port)) {m_pPlainText->appendPlainText(QStringLiteral("**已成功绑定"));m_pPlainText->appendPlainText(QStringLiteral("绑定端口：") + QString::number(m_pUdpSocket->localPort()));//使能m_pActBindPort->setEnabled(false);m_pActUnbindPort->setEnabled(true);} else {m_pPlainText->appendPlainText(QStringLiteral("绑定失败"));}
}void MainWindow::slotActUnbindPort() {m_pUdpSocket->abort();  //解除绑定m_pPlainText->appendPlainText(QStringLiteral("**已解除绑定"));m_pActBindPort->setEnabled(true);m_pActUnbindPort->setEnabled(false);
}void MainWindow::slotActClearText() { m_pPlainText->clear(); }void MainWindow::slotActQuit() {QMessageBox::StandardButton button = QMessageBox::question(this, "", QStringLiteral("是否要退出？"));if (button == QMessageBox::StandardButton::Yes)this->close();
}void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState) {switch (socketState){case QAbstractSocket::UnconnectedState: m_pLabState->setText(QStringLiteral("socket状态：UnconnectedState")); break;case QAbstractSocket::HostLookupState: m_pLabState->setText(QStringLiteral("socket状态：HostLookupState")); break;case QAbstractSocket::ConnectingState: m_pLabState->setText(QStringLiteral("socket状态：ConnectingState")); break;case QAbstractSocket::ConnectedState: m_pLabState->setText(QStringLiteral("socket状态：ConnectedState")); break;case QAbstractSocket::BoundState: m_pLabState->setText(QStringLiteral("socket状态：BoundState")); break;case QAbstractSocket::ClosingState: m_pLabState->setText(QStringLiteral("socket状态：ClosingState")); break;default: break;}}void MainWindow::slotBtnSend()
{QString msg = m_pLineEdit->text();QByteArray str = msg.toUtf8();QString targetIp = m_pComboTargetAddr->currentText();  //目标IPQHostAddress targetAddr(targetIp);quint16 targetPort = m_pSpinTargetPort->value();  //目标端口m_pUdpSocket->writeDatagram(str, targetAddr, targetPort);m_pPlainText->appendPlainText("[out] " + msg);m_pLineEdit->clear();m_pLineEdit->setFocus();}void MainWindow::slotBtnBroad()
{QString msg = m_pLineEdit->text();QByteArray str = msg.toUtf8();quint16 targetPort = m_pSpinTargetPort->value();m_pUdpSocket->writeDatagram(str, QHostAddress::Broadcast, targetPort);m_pPlainText->appendPlainText("[out] " + msg);m_pLineEdit->clear();m_pLineEdit->setFocus();}void MainWindow::slotSocketReadyRead()
{while (m_pUdpSocket->hasPendingDatagrams()){QByteArray dataGram;dataGram.resize(m_pUdpSocket->pendingDatagramSize());QHostAddress peerAddress;quint16 peerPort;m_pUdpSocket->readDatagram(dataGram.data(), dataGram.size(), &peerAddress, &peerPort);QString str = dataGram.data();QString peer = "[From " + peerAddress.toString() + ":" + QString::number(peerPort) + "]";m_pPlainText->appendPlainText(peer + str);}
}QString MainWindow::getLocalIP() {QString hostName = QHostInfo::localHostName();QHostInfo hostInfo = QHostInfo::fromName(hostName);QString localIP = "";QList<QHostAddress> addrList = hostInfo.addresses();if (!addrList.isEmpty()) {for (int i = 0; i < addrList.size(); i++) {QHostAddress addr = addrList.at(i);if (QAbstractSocket::IPv4Protocol == addr.protocol()) {localIP = addr.toString();break;}}}return localIP;
}

结果： 

 发现自己用UI设计时，发送信息总会出现两个发送信号，并且有一个是空白的，暂时还没有找到问题所在之处，嘤嘤嘤~(/≧▽≦)/

5. UDP组播代码示例

5.1 组播的特性

组播报文的目的地址使用D类IP地址，D类地址不能出现在IP报文的地址字段。用同一个IP多播地址接收多播数据报的所有主机构成一个组，称为多播组（或组播组）。所有的信息接收者都加入一个组内，并且一旦加入后，流向组地址的数据报立即开始向接收者传输，组中的所有的成员都能接收到数据报。组中的成员是动态的，主机可以在任何人时间加入和离开组。

关于组播IP地址，有以下约定：

224.0.0.0 ~ 224.0.0.255   为预留的组播地址（永久组地址），地址224.0.0.0保留不做分配，其他地址供路由协议使用。
224.0.1.0 ~ 224.0.1.255   是公用组播地址，可以用于Internet。
224.0.2.0 ~ 238.255.255.255     为用户可用的组播地址（临时组地址），全网范围内有效。
239.0.0.0 ~ 239.255.255.255     为本地管理组播地址，仅在特定的本地范围内有效。所以，若是在家庭或办公室局域网内测试UDP组播功能，可以使用这些IP。
原文链接：https://blog.csdn.net/WL0616/article/details/129050373

常量定义	值	描述
QUdpSocket::ShareAddress	0x1	1、允许其他服务绑定同样的地址和端口 2、当多进程通过监听同一地址和端口，进而共享单个服务的负载时，将十分有用(例如：一个拥有几个预先建立的监听者的WEB服务器能够改善响应时间)。不过，由于任何服务都允许重新绑定(rebind)，该选项应该引起某些安全上的考虑 3、需要注意的是，把该选项和ReuseAddressHint结合，也会允许你的服务重新绑定一个已存在的共享地址 4、在Unix上，该选项等同于SO_REUSEADDR；在Windows上，该选项被忽略
QUdpSocket::DontShareAddress	0x2	1、采用专有的方式绑定某个地址和端口，其他任何服务都不能再重新绑定 2、通过该选项，确保绑定成功，指定的服务将是地址和端口唯一监听者，就算是拥有ReuseAddressHint的服务也不允许重新绑定 3、在安全性上，该选项优于ShareAddress，但是在某些操作系统上需要管理员的权限才能运行 4、在Unix和Mac OS上，绑定地址和端口的默认行为是非共享，所以该选项会被忽略；在Windows上，等同于SO_EXCLUSIVEADDRUSE套接字选项
QUdpSocket::ReuseAddressHint	0x4	1、为QUdpSocke提供提示，即在地址和端口已经被其他套接字绑定的情况下，也应该试着重新绑定 2、在Unix上，该选项被忽略；在Windows上等同于SO_REUSEADDR 套接字选项
QUdpSocket::DefaultForPlatform	0x0	1、当前平台的默认选项 2、在Unix和Mac OS上，该选项等同于DontShareAddress + ReuseAddressHint；在Windows上等同于ShareAddress

5.2主要程序 

.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QAction>
#include <QComboBox>
#include <QHBoxLayout>
#include <QHostInfo>
#include <QLabel>
#include <QLineEdit>
#include <QMainWindow>
#include <QMessageBox>
#include <QPlainTextEdit>
#include <QPushButton>
#include <QRegExp>
#include <QSpinBox>
#include <QUdpSocket>
#include <QVBoxLayout>namespace Ui {class MainWindow;
}class MainWindow : public QMainWindow {Q_OBJECTpublic:explicit MainWindow(QWidget* parent = 0);~MainWindow();private slots:void slotActJoinMulti();void slotActLeaveMulti();void slotActClearText();void slotActQuit();void slotSocketStateChanged(QAbstractSocket::SocketState socketState);void slotBtnMultiMsg();void slotReadyRead();private:Ui::MainWindow* ui;QAction* m_pActJoinMulti;QAction* m_pActLeaveMulti;QAction* m_pActClearText;QAction* m_pActQuit;QWidget* m_pCentralWidget;QLabel* m_pLabPort;QLabel* m_pLabAddr;QSpinBox* m_pSpinPort;QComboBox* m_pComboAddr;QLineEdit* m_pLineEdit;QPushButton* m_pBtnSendMulti;QPlainTextEdit* m_pPlainText;QLabel* m_pLabState;QUdpSocket* m_pUdpSocket;QHostAddress m_multicastAddr;QString getLocalIP();
};#endif  // MAINWINDOW_H

.cpp

#include "mainwindow.h"#include "ui_mainwindow.h"MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent), ui(new Ui::MainWindow) {ui->setupUi(this);this->setWindowTitle(QStringLiteral("UDP Multicast"));//工具栏ui->mainToolBar->setToolButtonStyle(Qt::ToolButtonTextBesideIcon);m_pActJoinMulti = new QAction(QIcon(":/new/prefix1/res/添加群组.png"), QStringLiteral("加入组播"), this);m_pActLeaveMulti = new QAction(QIcon(":/new/prefix1/res/退出群组.png"), QStringLiteral("退出组播"), this);m_pActClearText = new QAction(QIcon(":/new/prefix1/res/清空.png"), QStringLiteral("清空文本"), this);m_pActQuit = new QAction(QIcon(":/new/prefix1/res/退出.png"), QStringLiteral("退出"), this);ui->mainToolBar->addAction(m_pActJoinMulti);ui->mainToolBar->addAction(m_pActLeaveMulti);ui->mainToolBar->addSeparator();ui->mainToolBar->addAction(m_pActClearText);ui->mainToolBar->addSeparator();ui->mainToolBar->addAction(m_pActQuit);//界面布局m_pCentralWidget = new QWidget(this);m_pLabPort = new QLabel(QStringLiteral("组播端口"), m_pCentralWidget);m_pSpinPort = new QSpinBox(m_pCentralWidget);m_pSpinPort->setMinimum(1);m_pSpinPort->setMaximum(65535);m_pSpinPort->setValue(3200);m_pLabAddr = new QLabel(QStringLiteral("组播地址"), m_pCentralWidget);m_pComboAddr = new QComboBox(m_pCentralWidget);m_pComboAddr->setEditable(true);  //下拉框可编辑输入m_pComboAddr->addItem("239.0.0.1");// 正则匹配 D类IP：224.0.0.0~239.255.255.255// .必须使用转义字符\，否则.会匹配任意字符// C++中"\"在字符串中表示要用"\\"// 是 - 不是 ~ ； 是[0-9]不是[0~9]QRegExp regExp("^(22[4-9]|23[0-9])(\\.((\\d)|([1-9]\\d)|(1\\d{2})|(2[0-4]\\d)|(25[0-5]))){3}$");QValidator* pValidator = new QRegExpValidator(regExp, this);m_pComboAddr->setValidator(pValidator);QHBoxLayout* HLay1 = new QHBoxLayout();HLay1->addWidget(m_pLabPort, 1, Qt::AlignRight);HLay1->addWidget(m_pSpinPort, 1);HLay1->addWidget(m_pLabAddr, 1, Qt::AlignRight);HLay1->addWidget(m_pComboAddr, 2);m_pLineEdit = new QLineEdit(m_pCentralWidget);m_pBtnSendMulti = new QPushButton(QStringLiteral("组播消息"), m_pCentralWidget);QHBoxLayout* HLay2 = new QHBoxLayout();HLay2->addWidget(m_pLineEdit, 4);HLay2->addWidget(m_pBtnSendMulti, 1);m_pPlainText = new QPlainTextEdit(m_pCentralWidget);QVBoxLayout* VLay = new QVBoxLayout(m_pCentralWidget);VLay->addLayout(HLay1);VLay->addLayout(HLay2);VLay->addWidget(m_pPlainText);this->setCentralWidget(m_pCentralWidget);this->setLayout(VLay);//状态栏m_pLabState = new QLabel(QStringLiteral("socket状态："), this);m_pLabState->setMinimumWidth(150);ui->statusBar->addWidget(m_pLabState);QString str = getLocalIP();this->setWindowTitle(this->windowTitle() + "---IP:" + str);m_pUdpSocket = new QUdpSocket(this);m_pUdpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption, 1);// connectconnect(m_pActJoinMulti, &QAction::triggered, this, &MainWindow::slotActJoinMulti);connect(m_pActLeaveMulti, &QAction::triggered, this, &MainWindow::slotActLeaveMulti);connect(m_pActClearText, &QAction::triggered, this, &MainWindow::slotActClearText);connect(m_pActQuit, &QAction::triggered, this, &MainWindow::slotActQuit);connect(m_pUdpSocket, &QUdpSocket::stateChanged, this, &MainWindow::slotSocketStateChanged);connect(m_pBtnSendMulti, &QPushButton::clicked, this, &MainWindow::slotBtnMultiMsg);connect(m_pUdpSocket, &QUdpSocket::readyRead, this, &MainWindow::slotReadyRead);
}MainWindow::~MainWindow() { delete ui; }void MainWindow::slotActJoinMulti() {QString ip = m_pComboAddr->currentText();m_multicastAddr = QHostAddress(ip);quint16 multicastPort = m_pSpinPort->value();if (m_pUdpSocket->bind(QHostAddress::AnyIPv4, multicastPort, QUdpSocket::ShareAddress)) {m_pUdpSocket->joinMulticastGroup(m_multicastAddr);  //加入多播组m_pPlainText->appendPlainText("**加入组播成功");m_pPlainText->appendPlainText("**组播地址IP：" + ip);m_pPlainText->appendPlainText("**绑定端口：" + QString::number(multicastPort));m_pActJoinMulti->setEnabled(false);m_pActLeaveMulti->setEnabled(true);m_pComboAddr->setEditable(false);} else {m_pPlainText->appendPlainText("**绑定端口失败");}
}void MainWindow::slotActLeaveMulti() {m_pUdpSocket->leaveMulticastGroup(m_multicastAddr);  //退出组播m_pUdpSocket->abort();                               //解除绑定m_pActJoinMulti->setEnabled(true);m_pActLeaveMulti->setEnabled(false);m_pComboAddr->setEnabled(true);m_pComboAddr->setEditable(true);m_pPlainText->appendPlainText("**已退出组播，解除端口绑定");
}void MainWindow::slotActClearText() { m_pPlainText->clear(); }void MainWindow::slotActQuit() {QMessageBox::StandardButton button = QMessageBox::question(this, "", "是否退出？");if (QMessageBox::StandardButton::Yes == button) {this->close();}
}void MainWindow::slotSocketStateChanged(QAbstractSocket::SocketState socketState) {// case并不包含所有的情况，因为没有写listening的情况，所以就需要写defaultswitch (socketState) {case QAbstractSocket::UnconnectedState: m_pLabState->setText("socket状态：UnconnectedState"); break;case QAbstractSocket::HostLookupState: m_pLabState->setText("socket状态：HostLookupState"); break;case QAbstractSocket::ConnectingState: m_pLabState->setText("socket状态：ConnectingState"); break;case QAbstractSocket::ConnectedState: m_pLabState->setText("socket状态：ConnectedState"); break;case QAbstractSocket::BoundState: m_pLabState->setText("socket状态：BoundState"); break;case QAbstractSocket::ClosingState: m_pLabState->setText("socket状态：ClosingState"); break;default: break;}
}void MainWindow::slotBtnMultiMsg() {QString msg = m_pLineEdit->text();QByteArray str = msg.toUtf8();quint16 multiPort = m_pSpinPort->value();m_pUdpSocket->writeDatagram(str, m_multicastAddr, multiPort);m_pPlainText->appendPlainText("[multicast] " + msg);m_pLineEdit->clear();m_pLineEdit->setFocus();
}void MainWindow::slotReadyRead() {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) + "] ";m_pPlainText->appendPlainText(peer + str);qDebug() << m_pUdpSocket->peerAddress();qDebug() << m_pUdpSocket->localAddress().toString();qDebug() << m_pUdpSocket->localPort();}
}QString MainWindow::getLocalIP() {QString localName = QHostInfo::localHostName();QHostInfo hostInfo = QHostInfo::fromName(localName);QList<QHostAddress> addrList = hostInfo.addresses();QString localIP = "";if (!addrList.isEmpty()) {for (int i = 0; i < addrList.size(); i++) {QHostAddress addr = addrList.at(i);if (QAbstractSocket::IPv4Protocol == addr.protocol()) {localIP = addr.toString();break;}}}return localIP;
}

结果： 

原文链接：https://blog.csdn.net/WL0616/article/details/129050373