qt中，每连接一次tcp就往文件中写一次时间的代码

在Qt中，如果你想要每次成功连接TCP后都向文件中写入当前的时间，你可以使用QIODevice、QTcpSocket以及QDateTime等类来实现。这里是一个简单的示例代码片段：

#include <QObject>
#include <QTcpSocket>
#include <QFile>
#include <QDateTime>

class TcpConnectionHandler : public QObject
{
    Q_OBJECT

public:
    explicit TcpConnectionHandler(QObject *parent = nullptr)
        : QObject(parent)
    {
        connect(&tcpSocket, &QTcpSocket::connected, this, &TcpConnectionHandler::onConnected);
        connect(&tcpSocket, &QTcpSocket::disconnected, this, &TcpConnectionHandler::onDisconnected);
    }

private slots:
    void onConnected()
    {
        QDateTime currentTime = QDateTime::currentDateTime();
        QString dateTimeStr = currentTime.toString("yyyy-MM-dd HH:mm:ss");

        QFile file("time_log.txt");
        if (file.open(QIODevice::Append | QIODevice::Text)) {
            QTextStream out(&file);
            out << "Connected at: " << dateTimeStr << "\n";
            file.close();
            qDebug() << "Time logged: " << dateTimeStr;
        } else {
            qWarning() << "Failed to open file for writing.";
        }
    }

    void onDisconnected()
    {
        // Write disconnection time here or handle accordingly
    }

signals:
    // If needed, you can emit a signal when connected or disconnected

};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    TcpConnectionHandler handler;
    QTcpServer server(&handler);
    server.listen(QHostAddress::Any, 12345);

    return app.exec();
}

在这个例子中，我们创建了一个`TcpConnectionHandler`类，当TCP连接建立时，会记录当前时间并追加到`time_log.txt`文件中。如果文件打开失败，会在控制台输出警告信息。