Test a local connection with Qt - c++

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
}

Answer 3

Use QT's QNetworkAccessManager class which provides networkAccessibleChanged Signal
and connect a slot to it
connect(&networkAccessManager, SIGNAL(networkAccessibleChanged(QNetworkAccessManager::NetworkAccessibility)), this, SLOT(onNetworkAccessibilityChanged(QNetworkAccessManager::NetworkAccessibility)));
it emits signal telling when the ethernet cable is unplugged