读取：

    QFile file(path);
    if(file.open(QIODevice::ReadOnly | QIODevice::Text)){
        QByteArray t = file.readAll();
        ui->t->setText(QString(t));//显示出来
        file.close();
    }

写入：

    QFile file(path);
    if(file.open(QIODevice::WriteOnly | QIODevice::Text)){
        file.write(data.toUtf8());
        file.close();
    }