QT5_Data type conversion

QString to int, double to QString assigned to label

    QString tempStr;
    QString valueStr=ui->radiusLineEdit->text();
    int valueInt = valueStr.toInt();
    double area=valueInt*valueInt*PI;
    ui->areaLabel_2->setText(tempStr.setNum(area));

QString to char *

   QByteArray ba = A(QString).toLatin1(); //A为Qstring类型
   char *t_b_d = ba.data();