qt modbus tcp缓存区的示例不使用modbus库

以下是一个使用Qt的示例代码，演示如何使用TCP套接字来实现Modbus TCP通信，并且不依赖于任何第三方Modbus库。

#include <QtNetwork>

// Modbus TCP 报文头
struct ModbusTcpHeader {
    quint16 transactionId;
    quint16 protocolId;
    quint16 length;
    quint8 unitId;
};

// Modbus TCP 请求报文体
struct ModbusTcpRequest {
    quint16 functionCode;
    quint16 startAddress;
    quint16 count;
};

// Modbus TCP 响应报文体
struct ModbusTcpResponse {
    quint8 byteCount;
    QByteArray data;
};

class ModbusTcpClient : public QObject
{
    Q_OBJECT
public:
    explicit ModbusTcpClient(QObject *parent = nullptr);

    void connectToServer(const QString &host, quint16 port);

    bool readHoldingRegisters(quint8 unitId, quint16 startAddress, quint16 count, QVector<quint16> &values);

private slots:
    void onConnected();
    void onDisconnected();
    void onError(QAbstractSocket::SocketError error);
    void onReadyRead();

private:
    void sendRequest(const QByteArray &data);
    bool parseResponse(const QByteArray &data, QVector<quint16> &values);

private:
    QTcpSocket *m_socket;
    quint16 m_transactionId;
};

ModbusTcpClient::ModbusTcpClient(QObject *parent) : QObject(parent),
    m_socket(new QTcpSocket(this)),
    m_transactionId(0)
{
    connect(m_socket, &QTcpSocket::connected, this, &ModbusTcpClient::onConnected);
    connect(m_socket, &QTcpSocket::disconnected, this, &ModbusTcpClient::onDisconnected);
    connect(m_socket, static_cast<void(QAbstractSocket::*)(QAbstractSocket::SocketError)>(&QAbstractSocket::error), this, &ModbusTcpClient::onError);
    connect(m_socket, &QTcpSocket::readyRead, this, &ModbusTcpClient::onReadyRead);
}

void ModbusTcpClient::connectToServer(const QString &host, quint16 port)
{
    m_socket->connectToHost(host, port);
}

bool ModbusTcpClient::readHoldingRegisters(quint8 unitId, quint16 startAddress, quint16 count, QVector<quint16> &values)
{
    ModbusTcpHeader header;
    header.transactionId = ++m_transactionId;
    header.protocolId = 0;
    header.length = 6;
    header.unitId = unitId;

    ModbusTcpRequest request;
    request.functionCode = 3;
    request.startAddress = startAddress;
    request.count = count;

    QByteArray requestData;
    requestData.append(reinterpret_cast<const char *>(&header), sizeof(header));
    requestData.append(reinterpret_cast<const char *>(&request), sizeof(request));

    sendRequest(requestData);

    values.clear();

    if (m_socket->waitForReadyRead()) {
        QByteArray responseData = m_socket->readAll();
        return parseResponse(responseData, values);
    } else {
        return false;
    }
}

void ModbusTcpClient::onConnected()
{
    qDebug() << "Connected to Modbus TCP server";
}

void ModbusTcpClient::onDisconnected()
{
    qDebug() << "Disconnected from Modbus TCP server";
}

void ModbusTcpClient::onError(QAbstractSocket::SocketError error)
{
    qDebug() << "Modbus TCP socket error:" << error << "-" << m_socket->errorString();
}

void ModbusTcpClient::onReadyRead()
{
    qDebug() << "Modbus TCP socket ready to read";
}

void ModbusTcpClient::sendRequest(const QByteArray &data)
{
    m_socket->write(data);
}

bool ModbusTcpClient::parseResponse(const QByteArray &data, QVector<quint16> &values)
{
    ModbusTcpHeader header = *reinterpret_cast<const ModbusTcpHeader *>(data.constData());
    if (header.unitId != 1 || header.length < 3) {
        return false;
    }

    ModbusTcpResponse response;
    response.byteCount = data[9];
    response.data = data.mid(10);

    if (response.byteCount != response.data.length()) {
        return false;
    }

    for (int i = 0; i < response.byteCount; i += 2) {
        quint16 value = (static_cast<quint8>(response.data[i]) << 8) | static_cast<quint8>(response.data[i + 1]);
        values.append(value);
    }

    return true;
}

使用示例：

ModbusTcpClient client;
client.connectToServer("192.168.1.100", 502);

QVector<quint16> values;
bool success = client.readHoldingRegisters(1, 0, 10, values);

if (success) {
    qDebug() << "Read holding registers succeeded:" << values;
} else {
    qDebug() << "Read holding registers failed";
}