Programmatically check whether my machine has internet access or not

Question

How can I programmatically check whether my machine has internet access or not using C/C++, is it just a matter of pinging an IP? How does NIC do it ? I mean something like

Answer 1

In addition to the InternetCheckConnection() function, The Win32 API has a function ( InternetGetConnectedState() ) which returns a true/false for (the availability of) some form of internet connectivity:

https://msdn.microsoft.com/en-us/library/windows/desktop/aa384702(v=vs.85).aspx

It also tells you what type of connection to the internet you have(LAN, modem, Proxy etc) - which can often be very handy to know.

Answer 2

If you work on Windows, just try this

#include <iostream>
#include <windows.h> 
#include <wininet.h>
using namespace std;

int main(){

if(InternetCheckConnection(L"http://www.google.com",FLAG_ICC_FORCE_CONNECTION,0))
{
        cout << "connected to internet";
}

return 0;
}

Answer 3

There is nothing of that sort I think, but you can try this:

The easiest way is to try to connect to a known outside IP address.

If it fails in Windows, the connect function will return SOCKET_ERROR, and WSAGetLastError will usually return WSAEHOSTUNREACH (meaning the packet couldn't be sent to the host).

In Linux, you'll get back a -1, and errno will be ENETUNREACH. Some useful links:

1. Link for Windows Sockets

2. Link for Linux/Unix sockets

Answer 4

According to Microsoft API document InternetCheckConnection is deprecated.

[InternetCheckConnection is available for use in the operating systems specified in the Requirements section. It may be altered or unavailable in subsequent versions. Instead, use NetworkInformation.GetInternetConnectionProfile or the NLM Interfaces. ]

Instead of this API we can use INetworkListManager interface to check whether Internet is connected or not for windows platform.

Here below is the win32 codebase :

#include <iostream>
#include <ObjBase.h>      // include the base COM header
#include <Netlistmgr.h>

// Instruct linker to link to the required COM libraries
#pragma comment(lib, "ole32.lib")

using namespace std;

enum class INTERNET_STATUS
{
    CONNECTED,
    DISCONNECTED,
    CONNECTED_TO_LOCAL,
    CONNECTION_ERROR
};

INTERNET_STATUS IsConnectedToInternet();

int main()
{
    INTERNET_STATUS connectedStatus = INTERNET_STATUS::CONNECTION_ERROR;
    connectedStatus = IsConnectedToInternet();
    switch (connectedStatus)
    {
    case INTERNET_STATUS::CONNECTED:
        cout << "Connected to the internet" << endl;
        break;
    case INTERNET_STATUS::DISCONNECTED:
        cout << "Internet is not available" << endl;
        break;
    case INTERNET_STATUS::CONNECTED_TO_LOCAL:
        cout << "Connected to the local network." << endl;
        break;
    case INTERNET_STATUS::CONNECTION_ERROR:
    default:
        cout << "Unknown error has been occurred." << endl;
        break;
    }
}

INTERNET_STATUS IsConnectedToInternet()
{
    INTERNET_STATUS connectedStatus = INTERNET_STATUS::CONNECTION_ERROR;
    HRESULT hr = S_FALSE;

    try
    {
        hr = CoInitialize(NULL);
        if (SUCCEEDED(hr))
        {
            INetworkListManager* pNetworkListManager;
            hr = CoCreateInstance(CLSID_NetworkListManager, NULL, CLSCTX_ALL, __uuidof(INetworkListManager), (LPVOID*)&pNetworkListManager);
            if (SUCCEEDED(hr))
            {
                NLM_CONNECTIVITY nlmConnectivity = NLM_CONNECTIVITY::NLM_CONNECTIVITY_DISCONNECTED;
                VARIANT_BOOL isConnected = VARIANT_FALSE;
                hr = pNetworkListManager->get_IsConnectedToInternet(&isConnected);
                if (SUCCEEDED(hr))
                {
                    if (isConnected == VARIANT_TRUE)
                        connectedStatus = INTERNET_STATUS::CONNECTED;
                    else
                        connectedStatus = INTERNET_STATUS::DISCONNECTED;
                }

                if (isConnected == VARIANT_FALSE && SUCCEEDED(pNetworkListManager->GetConnectivity(&nlmConnectivity)))
                {
                    if (nlmConnectivity & (NLM_CONNECTIVITY_IPV4_LOCALNETWORK | NLM_CONNECTIVITY_IPV4_SUBNET | NLM_CONNECTIVITY_IPV6_LOCALNETWORK | NLM_CONNECTIVITY_IPV6_SUBNET))
                    {
                        connectedStatus = INTERNET_STATUS::CONNECTED_TO_LOCAL;
                    }
                }

                pNetworkListManager->Release();
            }
        }

        CoUninitialize();
    }
    catch (...)
    {
        connectedStatus = INTERNET_STATUS::CONNECTION_ERROR;
    }

    return connectedStatus;
}

Answer 5

The following code will work, if you're on windows:

#include <iostream>
#include <windows.h>

int main(){

  if (system("ping www.google.com")){
          std::cout<<"\nNot connnected to the internet\n\n";
  }
  else{
          std::cout<<"\nConnected to the internet\n\n";

  }
  system("pause");
  return 0;
}

Answer 6

There is actually a very smart way including code snip here.

It basically using the cmd option: While in CMD hit: route print.

This will map routing table with an array and will look for 0.0.0.0 as an available internet connection.

I used it with a while(true){//the code in here } //check for inet connection , else will sleep for 10 mins and check again