QNetworkInformation Class

#include <QCoreApplication>
#include <QNetworkInformation>
#include <QDebug>

void onReachabilityChanged(QNetworkInformation::Reachability reachability) {
    switch (reachability) {
    case QNetworkInformation::Reachability::Unknown:
        qDebug() << "Network reachability is unknown.";
       break;
    case QNetworkInformation::Erreichbarkeit::Nicht verbunden:
        qDebug() << "Network is disconnected.";
       break;
    case QNetworkInformation::Erreichbarkeit::Lokal:
        qDebug() << "Network is locally reachable.";
       break;
    case QNetworkInformation::Erreichbarkeit::Standort:
        qDebug() << "Network can reach the site.";
       break;
    case QNetworkInformation::Erreichbarkeit::Online:
        qDebug() << "Network is online.";
       break;
    }
}

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    // Prüfen, ob QNetworkInformation unterstützt wird
    if (!QNetworkInformation::loadDefaultBackend()) {
        qWarning() << "QNetworkInformation is not supported on this platform or backend.";
       return 1;
    }

    QNetworkInformation* netInfo = QNetworkInformation::instance();

    // Verbindung zum Signal „reachabilityChanged“ herstellen
    QObject::connect(netInfo, &QNetworkInformation::reachabilityChanged,
                     &onReachabilityChanged);

    // Anfangsstatus ausgeben
    onReachabilityChanged(netInfo->reachability());

    return a.exec();
}

// Einfache Hilfsfunktion zur Feststellung, ob eine IP-Adresse „lokal“ ist
bool isLocalAddress(const QHostAddress&address)
{
    return address.isInSubnet(QHostAddress("192.168.0.0"), 16)||
           address.isInSubnet(QHostAddress("10.0.0.0"), 8)     ||
           address.isInSubnet(QHostAddress("172.16.0.0"), 12)  ||
           address.isLoopback();
}

int main(int argc, char *argv[])
{
    ...
    // Ziel-IP-Adresse (Standard: Google-DNS)
    QString targetIpStr = argc > 1 ? argv[1]: "8.8.8.8";
    QHostAddress targetIp(targetIpStr);

    if (targetIp.isNull()) {
        qWarning() << "Invalid IP address:" << targetIpStr;
       return 1;
    }

    // Festlegen, welche Erreichbarkeitsstufe für das Ziel erforderlich ist
    QNetworkInformation::Erreichbarkeitsstufe requiredReachability =
        isLocalAddress(targetIp)
            ? QNetworkInformation::Reachability::Local
            : QNetworkInformation::Reachability::Online;

    // Die aktuell vom System gemeldete Erreichbarkeit abrufen
    QNetworkInformation::Reachability currentReachability = networkInfo->reachability();

    qDebug() << "Target IP:" << targetIp.toString();
    qDebug() << "Target is considered"
            << (isLocalAddress(targetIp) ? "local/site.": "external/online.");
    qDebug() << "Required reachability level:" << requiredReachability;
    qDebug() << "Current reachability:" << currentReachability;

   if (aktuelle Erreichbarkeit < erforderliche Erreichbarkeit) {
        qWarning() << "Current network state may not allow reaching the target address.";
    } else {
        qDebug() << "Target may be reachable based on current network state.";
    }
    ...