QT中，对于大小端UDP网络发送的demo，帧头帧尾

简单demo:

发送端：

#include 
#include 

#pragma pack(1)
struct Test
{
    unsigned char   t1:1;
    unsigned char   t2:2;
    unsigned char   t3:3;
    unsigned char   t4:2;
    quint8    a = 1;
    quint16   b = 2;
    quint16   c = 3;
    //double    b = 2;
    quint8    d = 4;
    quint8    e = 1;
};
#pragma pack(pop)

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QByteArray temp_byte_array;
    Test test;
    test.b = qToBigEndian(test.b);
    test.c = qToBigEndian(test.c);
    test.b = qToBigEndian(test.b);
    test.t1 = 0x1;
    test.t2 = 0x2;
    test.t3 = 0x3;
    test.t4 = 0x2;

    QUdpSocket *m_pUdpSocket = new QUdpSocket();
    m_pUdpSocket->bind(QHostAddress("127.0.0.1"),8002);
    QByteArray frame = QByteArray((char *)&test, sizeof(Test));
    m_pUdpSocket->writeDatagram(frame, QHostAddress("127.0.0.1"), 8001);

    return 0;
}

接收：

#include 
#include 

#pragma pack(1)
struct Test
{
    unsigned char   t1:1;
    unsigned char   t2:2;
    unsigned char   t3:3;
    unsigned char   t4:2;
    quint8    a = 0x1;
    quint16   b = 0x2;
    quint16   c = 0x3;
    //double    b = 2;
    quint8    d = 0x4;
    quint8    e = 0x1;
};
#pragma pack(pop)

int main(int argc, char *argv[])
{

    QApplication app(argc, argv);
    QUdpSocket *m_pUdpSocket = new QUdpSocket();
    m_pUdpSocket->bind(QHostAddress("127.0.0.1"),8001);
    QObject::connect(m_pUdpSocket,&QUdpSocket::readyRead,[=](){
        QByteArray frame;
        frame.resize(m_pUdpSocket->pendingDatagramSize());
        // 接收数据报，将其存放到datagram中
        m_pUdpSocket->readDatagram(frame.data(), frame.size());
        struct Test *pFrame = (struct Test *)frame.data();
        qDebug()<<"a:"<a;
        qDebug()<<"b:"<b;
        qDebug()<<"c:"<c;
        qDebug()<<"d:"<d;
        qDebug()<<"*****************";
    });

    return app.exec();
}

有帧头帧尾：

发送：

#include 
#include 

// 以1字节对齐：
#pragma pack(1)
struct Test
{
    // 帧头 0xabcd
    unsigned short dataHead = 0xabcd;

    // 小于1字节：
    unsigned char   t1:1;
    unsigned char   t2:2;
    unsigned char   t3:3;
    unsigned char   t4:2;

    // 小于或者大于1字节
    quint8    a = 0x1;
    quint16   b = 0x2;
    quint16   c = 0x3;
    quint8    d = 0x4;
    quint8    e = 0x1;

    // 包尾 dcba
    unsigned short dataTail = 0xdcba;
};
#pragma pack(pop)

int main(int argc, char *argv[])
{

    QByteArray temp_byte_array;
    Test test;
    //test.b = qToBigEndian(test.b);
    //test.c = qToBigEndian(test.c);
    test.t1 = 0x1;
    test.t2 = 0x2;
    test.t3 = 0x3;
    test.t4 = 0x2;

    QUdpSocket *m_pUdpSocket = new QUdpSocket();
    m_pUdpSocket->bind(QHostAddress("127.0.0.1"),8002);
    QByteArray frame = QByteArray((char *)&test, sizeof(Test));
    m_pUdpSocket->writeDatagram(frame, QHostAddress("127.0.0.1"), 8001);

}

接受：

#include 
#include 

// 以1字节对齐：
#pragma pack(1)
struct Test
{
    // 帧头 0xabcd
    unsigned short dataHead = 0xabcd;

    // 小于1字节：
    unsigned char   t1:1;
    unsigned char   t2:2;
    unsigned char   t3:3;
    unsigned char   t4:2;

    // 小于或者大于1字节
    quint8    a = 0x1;
    quint16   b = 0x2;
    quint16   c = 0x3;
    quint8    d = 0x4;
    quint8    e = 0x1;

    // 包尾 dcba
    unsigned short dataTail = 0xdcba;
};
#pragma pack(pop)

int main(int argc, char *argv[])
{

    QApplication app(argc, argv);
    QUdpSocket *m_pUdpSocket = new QUdpSocket();
    m_pUdpSocket->bind(QHostAddress("127.0.0.1"),8001);
    QObject::connect(m_pUdpSocket,&QUdpSocket::readyRead,[=](){
        QByteArray frame;
        frame.resize(m_pUdpSocket->pendingDatagramSize());
        // 接收数据报，将其存放到datagram中
        m_pUdpSocket->readDatagram(frame.data(), frame.size());
        struct Test *pFrame = (struct Test *)frame.data();
        if(pFrame->dataHead == 0xabcd && pFrame->dataTail == 0xdcba)
        {
            qDebug()<<"接收到信息*********";
            qDebug()<<"a:"<a;
            qDebug()<<"b:"<b;
            qDebug()<<"c:"<c;
            qDebug()<<"d:"<d;
            qDebug()<<"*****************";
        }

    });

    return app.exec();
}

会发现，如果不是这个帧头和帧尾，就会出问题，只有帧头帧尾正确，才可以正常解析。

注意事项：

1. 结构体前后一定要加1字节对齐，否则可能会多出很多字节，比如你们可以自己尝试不加一字节对齐，然后加入double会增加多少的字节。

2. 接收的时候，不要使用readall() 。

3. 测试的时候，发送不要使用串口调试助手等工具，哪些会出问题。

4. 大小端：很多系统默认小端，如果需要转为大端发送数据，大于1字节的数据，需要使用qToBigEndian()来转换。