qt实现modbus tcp写入

以下是使用Qt实现Modbus TCP写入的示例代码：

#include <QtNetwork>
#include <QtEndian>
#include <QDebug>

class ModbusTcpClient : public QObject
{
    Q_OBJECT
public:
    ModbusTcpClient(QObject *parent = nullptr)
        : QObject(parent)
        , m_socket(new QTcpSocket(this))
    {
        connect(m_socket, &QTcpSocket::connected, this, &ModbusTcpClient::onSocketConnected);
        connect(m_socket, &QTcpSocket::disconnected, this, &ModbusTcpClient::onSocketDisconnected);
        connect(m_socket, &QTcpSocket::readyRead, this, &ModbusTcpClient::onSocketReadyRead);
        connect(m_socket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error), this, &ModbusTcpClient::onSocketError);
    }

    bool connectToHost(const QString &host, quint16 port)
    {
        m_socket->connectToHost(host, port);
        if (!m_socket->waitForConnected(5000)) {
            qWarning() << "Failed to connect to host:" << host << "port:" << port << "error:" << m_socket->errorString();
            return false;
        }
        return true;
    }

    bool writeCoil(quint16 address, bool value)
    {
        quint8 buffer[12] = { 0 };
        quint16 tid = 0x0001; // transaction id
        quint16 pid = 0x0000; // protocol id
        quint16 len = 0x0006; // pdu length
        quint8 uid = 0x01; // unit id
        quint16 fcode = 0x0005; // function code
        quint16 addr = qToBigEndian(address); // coil address
        quint16 val = qToBigEndian(value ? 0xFF00 : 0x0000); // coil value

        qToBigEndian(tid, buffer); // write transaction id
        qToBigEndian(pid, buffer + 2); // write protocol id
        qToBigEndian(len, buffer + 4); // write pdu length
        buffer[6] = uid; // write unit id
        qToBigEndian(fcode, buffer + 7); // write function code
        qToBigEndian(addr, buffer + 9); // write coil address
        qToBigEndian(val, buffer + 11); // write coil value

        qint64 bytesWritten = m_socket->write(reinterpret_cast<const char *>(buffer), sizeof(buffer));
        if (bytesWritten != sizeof(buffer)) {
            qWarning() << "Failed to write to socket:" << m_socket->errorString();
            return false;
        }
        if (!m_socket->waitForBytesWritten(5000)) {
            qWarning() << "Failed to wait for bytes written:" << m_socket->errorString();
            return false;
        }
        return true;
    }

signals:
    void connected();
    void disconnected();
    void error(QAbstractSocket::SocketError error);
    void dataReceived(const QByteArray &data);

private slots:
    void onSocketConnected()
    {
        emit connected();
    }

    void onSocketDisconnected()
    {
        emit disconnected();
    }

    void onSocketError(QAbstractSocket::SocketError error)
    {
        emit error(error);
    }

    void onSocketReadyRead()
    {
        QByteArray data = m_socket->readAll();
        emit dataReceived(data);
    }

private:
    QTcpSocket *m_socket;
};

使用示例：

ModbusTcpClient client;
if (client.connectToHost("192.168.1.100", 502)) {
    if (client.writeCoil(0x0001, true)) {
        qDebug() << "Write coil success.";
    } else {
        qDebug() << "Write coil failed.";
    }
} else {
    qDebug() << "Failed to connect to host.";
}

在上面的示例中，`ModbusTcpClient`类封装了Modbus TCP客户端。`connectToHost`方法用于连接到Modbus TCP服务器。`writeCoil`方法用于写入线圈的值。线圈地址和值通过参数传递。如果写入成功，则返回`true`，否则返回`false`。在`onSocketReadyRead`槽中，当从服务器收到数据时，会发出`dataReceived`信号。使用时，只需实例化`ModbusTcpClient`类，然后调用`connectToHost`和`writeCoil`方法即可。