如何通过qt代码解析modbustcp协议下的客户端报文

要解析Modbus TCP协议下的客户端报文，您需要使用Qt中的网络编程模块，例如QTcpSocket类。您可以使用QTcpSocket类创建一个TCP客户端，连接到Modbus TCP服务器，并发送Modbus TCP请求报文到服务器。

以下是一个简单的示例代码，可以帮助您解析Modbus TCP请求报文：

#include <QtNetwork/QTcpSocket>

void readModbusTCPResponse(QTcpSocket *socket)
{
    QByteArray data = socket->readAll();

    // Check if we have received at least 9 bytes
    if (data.size() < 9) {
        qDebug() << "Invalid Modbus TCP response";
        return;
    }

    // Extract the transaction ID, protocol ID, and length fields
    quint16 transactionId = (quint16)data.mid(0, 2).toUInt();
    quint16 protocolId = (quint16)data.mid(2, 2).toUInt();
    quint16 length = (quint16)data.mid(4, 2).toUInt();

    // Check if the length field matches the actual length of the data
    if (length != data.size() - 6) {
        qDebug() << "Invalid Modbus TCP response";
        return;
    }

    // Extract the unit ID, function code, and data fields
    quint8 unitId = (quint8)data.mid(6, 1).toUInt();
    quint8 functionCode = (quint8)data.mid(7, 1).toUInt();
    QByteArray responseData = data.mid(8);

    // Process the response data based on the function code
    switch (functionCode) {
    case 0x01: // Read Coils
    {
        // Process the response data for Read Coils function
        break;
    }
    case 0x02: // Read Discrete Inputs
    {
        // Process the response data for Read Discrete Inputs function
        break;
    }
    case 0x03: // Read Holding Registers
    {
        // Process the response data for Read Holding Registers function
        break;
    }
    case 0x04: // Read Input Registers
    {
        // Process the response data for Read Input Registers function
        break;
    }
    case 0x05: // Write Single Coil
    {
        // Process the response data for Write Single Coil function
        break;
    }
    case 0x06: // Write Single Register
    {
        // Process the response data for Write Single Register function
        break;
    }
    case 0x0F: // Write Multiple Coils
    {
        // Process the response data for Write Multiple Coils function
        break;
    }
    case 0x10: // Write Multiple Registers
    {
        // Process the response data for Write Multiple Registers function
        break;
    }
    default:
        qDebug() << "Unsupported Modbus TCP function code";
        break;
    }
}

void sendModbusTCPRequest(QTcpSocket *socket, quint8 unitId, quint8 functionCode, quint16 address, quint16 count)
{
    QByteArray requestData;

    // Build the Modbus TCP request packet
    QDataStream stream(&requestData, QIODevice::WriteOnly);
    stream.setByteOrder(QDataStream::BigEndian);

    quint16 transactionId = 0xABCD; // Your transaction ID
    quint16 protocolId = 0x0000; // Always set to zero for Modbus TCP
    quint16 length = 0x0006; // Length of the following data
    stream << transactionId << protocolId << length << unitId << functionCode << address << count;

    // Send the request packet to the Modbus TCP server
    socket->write(requestData);

    // Wait for the server to respond
    if (!socket->waitForReadyRead()) {
        qDebug() << "Modbus TCP request timed out";
        return;
    }

    // Read and process the server response
    readModbusTCPResponse(socket);
}

在上面的示例代码中，`sendModbusTCPRequest`函数用于发送Modbus TCP请求报文，`readModbusTCPResponse`函数用于解析Modbus TCP响应报文。您需要根据您要使用的Modbus TCP功能码来实现相应的响应数据处理代码。