Test a local connection with Qt

Question

Is there a way to check if a cable is not unplugged by using Qt ?

I know the Ip adress that I want to contact, at first I was thinking of doing a ping request on this Ip Adress, but it seems to be too much complicated for this simple task.

So I'm thinking that maybe, there is a simple function able to do this in QNetwork library.

I search on the Internet but all the solutions are not testing one particular IP.

Thanks for your help.

Answer 1

Is there a way to check if a cable is not unplugged by using Qt ?

You can achieve this for specified interface using QNetworkSession:

QNetworkConfigurationManager nwManager (this);
for (;;QThread::sleep (1) ) {
    bool isConfigurationFound {false};
    for (auto & configuration : nwManager.allConfigurations (/*QNetworkConfiguration::Active*/) ) {
        // Name depends on the environment: "Wired connection 1", "McDonaldsFreeWiFi", "Home", "eth0", "eth1", etc...
        if (isConfigurationFound = (configuration.name () == "eth0") ) {
            QNetworkSession session (configuration, this);
            session.open ();
            session.waitForOpened (/*timeout*/);

            qDebug () << "Session info:";
            qDebug () << "- usage: " << (session.isOpen () ? "Opened" : "Closed");
            qDebug () << "- state: " << (session.state  () == QNetworkSession::Connected ? "Connected" : "Not connected");

            break;
        }
    }
    qDebug () << (isConfigurationFound ? "" : "Configuration not found.");
}

If you launch this code with connected cable you get:

"Session info:" 
"- usage: Opened;" 
"- state: Connected;" 

If you unplugged cable you get:

"Session info:" 
"- usage: Closed" 
"- state: Not connected"

Here is full example (also available at GitLab):

CMakeLists.txt

cmake_minimum_required (VERSION 2.8.8)
project (NaQt)
find_package (Qt5Network)
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

set (NaQt_SOURCES ${PROJECT_SOURCE_DIR}/main.cpp)
set (NaQt_HEADERS ${PROJECT_SOURCE_DIR}/NetworkAnalyzer.h)
qt5_wrap_cpp (NaQt_HEADERS_MOC ${NaQt_HEADERS})

add_executable (
    naqt
    ${NaQt_SOURCES}
    ${NaQt_HEADERS_MOC}
)
target_link_libraries (
    naqt
    Qt5::Core
    Qt5::Network
)

main.cpp

#include <QtCore>
#include "NetworkAnalyzer.h"

int main (int argc, char * argv [])
{
    QCoreApplication application (argc, argv);
    NetworkAnalyzer networkAnalyzer (& application);
    return application.exec ();
}

NetworkAnalyzer.h

#ifndef QT_NETWORK_ANALYZER_H
#define QT_NETWORK_ANALYZER_H

#include <QThread>
#include <QNetworkConfigurationManager>
#include <QNetworkSession>
#include <QDebug>

class NetworkAnalyzer : public QObject
{
Q_OBJECT

public:
    NetworkAnalyzer (QObject * parent = nullptr)
    {
        QNetworkConfigurationManager nwManager (this);
        for (;;QThread::sleep (1) ) {
            bool isConfigurationFound {false};
            for (auto & configuration : nwManager.allConfigurations (/*QNetworkConfiguration::Active*/) ) {
                // Name depends on the environment: "Wired connection 1", "McDonaldsFreeWiFi", "Home", "eth0", "eth1", etc...
                if (isConfigurationFound = (configuration.name () == "eth0") ) {
                    QNetworkSession session (configuration, this);
                    session.open ();
                    session.waitForOpened (/*timeout*/);

                    qDebug () << "Session info:";
                    qDebug () << "- usage: " << (session.isOpen () ? "Opened" : "Closed");
                    qDebug () << "- state: " << (session.state  () == QNetworkSession::Connected ? "Connected" : "Not connected");

                    break;
                }
            }
            qDebug () << (isConfigurationFound ? "" : "Configuration not found.");
        }
    }
};

#endif//QT_NETWORK_ANALYZER_H

Answer 2

Try opening a socket to the specified IP address on a predefined port :

QTcpSocket tester;

tester.connectToHost(address, port);

if(tester.waitForConnected(3000)) {
    //Remote host is online
} else {
    //Remote host is offline
}