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 <QUdpSocket>
#include <QtEndian>#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 <QUdpSocket>
#include <QtEndian>#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:"<<pFrame->a;qDebug()<<"b:"<<pFrame->b;qDebug()<<"c:"<<pFrame->c;qDebug()<<"d:"<<pFrame->d;qDebug()<<"*****************";});return app.exec();
}

有帧头帧尾：

发送：

#include <QUdpSocket>
#include <QtEndian>// 以1字节对齐：
#pragma pack(1)
struct Test
{// 帧头 0xabcdunsigned 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 dcbaunsigned 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 <QUdpSocket>
#include <QtEndian>// 以1字节对齐：
#pragma pack(1)
struct Test
{// 帧头 0xabcdunsigned 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 dcbaunsigned 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:"<<pFrame->a;qDebug()<<"b:"<<pFrame->b;qDebug()<<"c:"<<pFrame->c;qDebug()<<"d:"<<pFrame->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。