使用UDP协议接收数据并读取数据报

Question

在帮助我使用 UDP 协议向某人正确发送数据的第一个主题之后，我在接收这些数据时遇到了问题。这个问题很奇怪，只有在我第一次启动发送数据的功能时才会出现。第一次，服务器只接收第一帧。但之后，如果我重新使用该功能，一切都会好的。

这是通过UDP协议发送数据的代码（我的数据是一个结构体）：

void MyUDP::sendUDP()
{
    //Structure to send
    typedef struct MyStructTag
    {
       int test1;
       bool test2;
       char test3;
    } MyStruct;

    MyStruct envoie;

    envoie.test1 = 1;
    envoie.test2 = true;
    envoie.test3 = 97;

    // Sends the datagram datagram
    // to the host address and at port.
    // qint64 QUdpSocket::writeDatagram(const QByteArray & datagram,
    //                      const QHostAddress & host, quint16 port)

    QByteArray buf;
    QDataStream s(&buf, QIODevice::WriteOnly);
    // The encoding is big endian by default, on all systems. You
    // can change it if you wish.
    if (false) s.setByteOrder(QDataStream::LittleEndian);
    s << (qint32)envoie.test1 << (quint8)envoie.test2 << (qint8)envoie.test3;

    //I'm sending 5 frames        

    socket->writeDatagram(buf, QHostAddress("10.100.14.79"), 4000);
    socket->writeDatagram(buf, QHostAddress("10.100.14.79"), 4000);
    socket->writeDatagram(buf, QHostAddress("10.100.14.79"), 4000);
    socket->writeDatagram(buf, QHostAddress("10.100.14.79"), 4000);
    socket->writeDatagram(buf, QHostAddress("10.100.14.79"), 4000);
}

这是允许我接收这些数据的函数：

void MyUDP::readyRead()
{

    QHostAddress sender;
    quint16 senderPort;

    // qint64 QUdpSocket::readDatagram(char * data, qint64 maxSize,
    //                 QHostAddress * address = 0, quint16 * port = 0)
    // Receives a datagram no larger than maxSize bytes and stores it in data.
    // The sender's host address and port is stored in *address and *port
    // (unless the pointers are 0).

    typedef struct MyStructTag
    {
       int test1;
       bool test2;
       char test3;

    } MyStruct;

    MyStruct recois;
    socket->readDatagram((char*)&recois, sizeof (recois), &sender, &senderPort);


    qDebug() << "Message from: " << sender.toString();
    qDebug() << "Message port: " << senderPort;
    qDebug() << "Message: " << recois.test3;
}

为什么我第一次启动 sendUDP 时只收到 1 帧？

Answer 1

有两个问题：

1. 在其中，readyRead您必须循环 whilesocket->hasPendingDatagrams()为 true。

2. QDataStream您必须在发送端和接收端都使用。

最后，你正在编写C++，你不应该使用C结构语法。重复的结构声明也会适得其反。您需要的是拥有MyStruct.

下面是一个完整的例子。

#include <QCoreApplication>
#include <QUdpSocket>
#include <QDataStream>
#include <QBasicTimer>

static const quint16 port = 4000;

class MyUDP : public QObject {
   Q_OBJECT
   QUdpSocket m_socket;
   QBasicTimer m_timer;

   void timerEvent(QTimerEvent*ev) {
      if (ev->timerId() != m_timer.timerId()) return;
      sendUDP();
   }
   void sendUDP();
public:
   MyUDP() {
      m_timer.start(1000, this);
      connect(&m_socket, SIGNAL(readyRead()), SLOT(readyRead()));
      m_socket.bind(QHostAddress::LocalHost, port);
   }
   Q_SLOT void readyRead();
};

struct MyStruct {
   int test1;
   bool test2;
   char test3;
   MyStruct() {}
   MyStruct(int t1, bool t2, char t3) : test1(t1), test2(t2), test3(t3) {}
};

template <typename T> T get(QDataStream & str) {
   T value;
   str >> value;
   return value;
}

QDataStream & operator<<(QDataStream & str, const MyStruct & m)
{
   return str << (qint32)m.test1 << (bool)m.test2 << (qint8)m.test3;
}

QDataStream & operator>>(QDataStream & str, MyStruct & m)
{
   m.test1 = get<qint32>(str);
   m.test2 = get<bool>(str);
   m.test3 = get<qint8>(str);
   return str;
}

void MyUDP::sendUDP()
{
   MyStruct envoie(1, true, 97);

   QByteArray buf;
   QDataStream s(&buf, QIODevice::WriteOnly);
   // The encoding is big endian by default, on all systems. You
   // can change it if you wish.
   if (false) s.setByteOrder(QDataStream::LittleEndian);
   s << envoie;

   for (int i = 0; i < 5; ++ i) {
      m_socket.writeDatagram(buf, QHostAddress::LocalHost, port);
   }
}

void MyUDP::readyRead()
{
   QHostAddress sender;
   quint16 senderPort;

   MyStruct recois;
   while (m_socket.hasPendingDatagrams()) {
      QByteArray buf(m_socket.pendingDatagramSize(), Qt::Uninitialized);
      QDataStream str(&buf, QIODevice::ReadOnly);
      m_socket.readDatagram(buf.data(), buf.size(), &sender, &senderPort);
      str >> recois;
      qDebug() << "Message from: " << sender;
      qDebug() << "Message port: " << senderPort;
      qDebug() << "Message: " << recois.test3;
   }
}

int main(int argc, char *argv[])
{
   QCoreApplication a(argc, argv);
   MyUDP udp;
   return a.exec();
}

#include "main.moc"