How to convert Q_ENUM to QString for QT > 5.11 most efficient way?

Question

I read several advices how to get an actual QString from a Q_ENUM value.

Below are 3 possible ways, I came up with, that are compilable constructs in QT5.11.1

What of them should one prefer and why?

void MainWindow::setErrorText(QCanBusDevice::CanBusError error)
{
    QString errorString;
    QDebug(&errorString) << error;
    ui->statusBar->showMessage("Error occured: " + errorString);

    // QT4 ?
    const QMetaObject& mo = QCanBusDevice::staticMetaObject;
    QMetaEnum me = mo.enumerator(mo.indexOfEnumerator("CanBusError"));
    QString errorStr(me.valueToKey(QCanBusDevice::UnconnectedState));
    ui->statusBar->showMessage("Error occured: " + errorStr);

   // From QT5?
   QString errorS(QMetaEnum::fromType<QCanBusDevice::CanBusError>().valueToKey(error));
   ui->statusBar->showMessage("Error occured: " + errorS);
}

Answer 1

QDebug should be used for logging and debugging. QDebug constructs a QTextStream and is quite expensive for what you're trying to do.

Using QMetaEnum is proper. You shouldn't be doing string concatenation the way you do, use tr for user visible strings, or QStringLiteral instead of tr elsewhere:

const auto errStr = QMetaEnum::fromType<QCanBusDevice::CanBusError>().valueToKey(error);
ui->statusBar->showMessage(tr("Error occured: %1").arg(errStr));

Answer 2

Another, more elegant way, is by using QVariant's toString() method:

QString errStr = QVariant::fromValue(error).toString();
ui->statusBar->showMessage("Error occured: " + errStr);