这篇博文的例子是说明如何在局域网上搭建广播包接收端。

这里使用了Qt Network API，搭建本地广播包接收端。

结构如下：

代码如下：

receiver.h

#ifndef RECEIVER_H
#define RECEIVER_H

#include <QWidget>

QT_BEGIN_NAMESPACE
class QLabel;
class QUdpSocket;
QT_END_NAMESPACE

class Receiver : public QWidget
{
    Q_OBJECT

public:
    explicit Receiver(QWidget *parent = nullptr);

private slots:
    void processPendingDatagrams();

private:
    QLabel *statusLabel = nullptr;
    QUdpSocket *udpSocket = nullptr;
};

#endif

main.cpp

#include <QApplication>

#include "receiver.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Receiver receiver;
    receiver.show();
    return app.exec();
}

receiver.cpp

#include <QtWidgets>
#include <QtNetwork>

#include "receiver.h"

Receiver::Receiver(QWidget *parent)
    : QWidget(parent)
{
    statusLabel = new QLabel(tr("Listening for broadcasted messages"));
    statusLabel->setWordWrap(true);

    auto quitButton = new QPushButton(tr("&Quit"));

//! [0]
    udpSocket = new QUdpSocket(this);
    udpSocket->bind(45454, QUdpSocket::ShareAddress);
//! [0]

//! [1]
    connect(udpSocket, SIGNAL(readyRead()),
            this, SLOT(processPendingDatagrams()));
//! [1]
    connect(quitButton, SIGNAL(clicked()), this, SLOT(close()));

    auto buttonLayout = new QHBoxLayout;
    buttonLayout->addStretch(1);
    buttonLayout->addWidget(quitButton);
    buttonLayout->addStretch(1);

    auto mainLayout = new QVBoxLayout;
    mainLayout->addWidget(statusLabel);
    mainLayout->addLayout(buttonLayout);
    setLayout(mainLayout);

    setWindowTitle(tr("Broadcast Receiver"));
}

void Receiver::processPendingDatagrams()
{
    QByteArray datagram;
//! [2]
    while (udpSocket->hasPendingDatagrams()) {
        datagram.resize(int(udpSocket->pendingDatagramSize()));
        udpSocket->readDatagram(datagram.data(), datagram.size());
        statusLabel->setText(tr("Received datagram: \"%1\"")
                             .arg(datagram.constData()));
    }
//! [2]
}

解释关键代码：

解释：广播报使用的是UDP，所以用的是QUdpSocket，并且绑定了端口45454。

解释：关联了信号与槽当网卡缓存中有数据时，调用对应的槽函数进行读取。

解释：当缓存区有数据时：hasPendingDatagrams()，然后就使用QByteArray获取读到的数据，最后设置到label上。