How to check an internet connection?

Someone else may have a better idea, but one way would be to attempt to open a connection to a URL that you know exists.  MFC contains CSocket which should allow you to do this.  Caveat: I'm not an MFC expert.

This seems a useful link
http://tangentsoft.net/wskfaq/examples/basics/

This seems to be working for me...I didn't try unplugging my internet connection.

#include "afxsock.h"
#include <iostream>

int main() {
   CSocket sock;
   try {
      sock.Connect("https://www.experts-exchange.com",8080);
      std::cout << "Internet is available." << std::endl;
   } catch (...) {
      std::cout << "Internet is not available." << std::endl;
   }
   sock.Close();
}

The most efficiant way is just calling 'InternetGetConnectedState()' (http://msdn2.microsoft.com/en-us/library/aa384702.aspx). See also http://support.microsoft.com/kb/242558 ("How To Detecting If You Have a Connection to the Internet"). Sockets can fail for a lot of reasons (wrong port, remote host down, no route to host).

The scoop is to

#include <Wininet.h>
#pragma comment(lib,"wininet.lib")
 
if (InternetGetConnectedState(INTERNET_CONNECTION_LAN | INTERNET_CONNECTION_MODEM) == FALSE)
{
    // Don't attempt connection or it will bring up the dialog
}

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That's a much better answer than the one I gave.  Thank you, jkr.

Since you are asking new questions again: Is there anything here that needs clarification?

To jkr :

1. Your answer, as usuall, is perfectly good, I didn't get the time to click the green button. I'll do it in a sec.

2. Why do you say that? What question I am asking again?