有qt写一段大妈两台上位机分别控制两台下位机，同一时刻两台上位机只能有一台能够控制

下面是一段基于 Qt 的示例代码，实现两台上位机分别控制两台下位机，同一时刻只允许一台上位机控制：

#include <QTcpSocket>
#include <QTcpServer>
#include <QObject>
#include <QList>

class Server : public QTcpServer
{
    Q_OBJECT

public:
    Server(QObject* parent = 0);

private slots:
    void processNewConnection();
    void processReadyRead();
    void removeClient();

private:
    QList<QTcpSocket*> clients;
    QTcpSocket* currentClient;
};

Server::Server(QObject* parent)
    : QTcpServer(parent)
{
    currentClient = NULL;
}

void Server::processNewConnection()
{
    QTcpSocket* client = nextPendingConnection();
    connect(client, SIGNAL(readyRead()), this, SLOT(processReadyRead()));
    connect(client, SIGNAL(disconnected()), this, SLOT(removeClient()));
    clients.append(client);
    qDebug() << "New client connected";
}

void Server::processReadyRead()
{
    QTcpSocket* client = qobject_cast<QTcpSocket*>(sender());
    if (client == NULL)
        return;
    QString message = client->readAll();
    if (message == "request_control")
    {
        // Check if there is already a client controlling
        if (currentClient != NULL && currentClient != client)
        {
            qDebug() << "Client rejected: another client is controlling";
            client->write("rejected");
            return;
        }

        // Grant control to this client
        currentClient = client;
        qDebug() << "Client granted control";
        client->write("granted");
    }
    else if (message == "release_control")
    {
        // Release control from this client
        currentClient = NULL;
        qDebug() << "Client released control";
    }
}

void Server::removeClient()
{
    QTcpSocket* client = qobject_cast<QTcpSocket*>(sender());
    if (client == NULL)
        return;
    clients.removeOne(client);
    if (client == currentClient)
        currentClient = NULL;
    qDebug() << "Client disconnected";
}

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

    Server server;
    if (!server.listen(QHostAddress::Any, 1234))
    {
        qDebug() << "Failed to start server";
        return 1;
    }

    qDebug() << "Server listening on port 1234";

    return app.exec();
}

上面的代码中，`Server` 类继承自 `QTcpServer`，用于监听客户端连接。当有新的客户端连接时，`Server::processNewConnection()` 方法会被调用，将客户端 Socket 添加到 `clients` 列表中，并连接 `readyRead()` 和 `disconnected()` 信号到相应的槽函数。`Server::processReadyRead()` 方法用于处理客户端发送的请求，如果请求是 `request_control`，则检查是否已经有客户端在控制，如果有，则拒绝请求，否则允许请求，并将 `currentClient` 设置为当前客户端。如果请求是 `release_control`，则释放控制权。`Server::removeClient()` 方法用于移除客户端 Socket，并将其从 `clients` 列表中删除。

在主函数中，创建 `Server` 实例，监听端口 1234，然后启动 Qt 事件循环。

注意：这只是一个简单的示例代码，实际应用中还需要考虑异常情况的处理，例如客户端连接断开、网络异常等。