BOOL IsInternetConnected()

Alot of times, programming internet applications you need to know wether the computer is connected to the internet?

In some occasions you can try to use RasEnumConnections, in most cases on a typical computer opened Ras Connection mean that the user is connected to the internet. However, this idea won't work in case the user is connected to internet not via Ras device or is connected to some kind of local network.

We try to use common sence here. Since internet is something abstract, lets decide that user which is connected to internet, is the one who can connect to www.microsoft.com.

First I wanted to use ping, but found a lot of troubles with it. Therefore, I have decided to use sockets "directly". I didn't want to write some fance code here, rather I have wrote a simple function you can cut & paste into your application.

Another problem adressed in the function that in some computer a try to establish internet connection will bring dialup dialog. The function solve it by temporary disabling the feature in the registry and enabling it back afterwards.

Pay attention to the comments.

BOOL YourClassHere::IsInternetConnected (void)
 int nCheck = AfxSocketInit();
 CSocket m_Server;
 HKEY hKey;
 DWORD dwDial, dwDialType = REG_DWORD, dwDialSize = 4;
 DWORD dwNew = 0;
 BOOL bResult = true;
 if ( RegOpenKeyEx ( HKEY_CURRENT_USER,
    Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings",
    ; // We cannot find the key. Handle this situation or just continue
 if ( RegQueryValueEx( hKey, "EnableAutodial", NULL, &dwDialType,
  (BYTE *) &dwDial, &dwDialSize ) != ERROR_SUCCESS )
  ; // We cannot find the value. Handle it.

 if ( dwDial ) { // We need to change the value, in order to make
            // a dialup window not to show up.
  if ( (nCheck = RegSetValueEx( hKey, "EnableAutodial", NULL,
   dwDialType, (BYTE *) &dwNew, dwDialSize )) != ERROR_SUCCESS)
  ; // Failed? We shouldn't get here. You decide how to handle it
 if ( !m_Server.Create() ) {                                                       
        // m_sError = _T( "Unable to create the socket." );
        bResult = false;

// You can use www.microsoft.com in order to check whether DNS is available
// or numeric IP otherwise 
 else if ( !m_Server.Connect( "www.microsoft.com", 80 ) ) {     //
        //m_sError = _T( "Unable to connect to server" );        
        bResult = false;
 if ( dwDial ) {
  if ( (nCheck = RegSetValueEx( hKey, "EnableAutodial", NULL,
   dwDialType, (BYTE *) &dwDial, dwDialSize )) != ERROR_SUCCESS)
  ; // Failed? We shouldn't get it. You decide how to handle this.
 RegCloseKey( hKey );
 return ( bResult );

I would like to thank Martin Tschepe for pointing me out this registry key.

Download source - 2KB


This article was originally published on June 16th, 1999

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