Acknowledgements
As many of you are aware, there is already an article on CodeGuru, ‘BOOL IsInternetConnected()’ by Ran, that contains a function that checks for Internet connectivity. However, while Ran’s version of this function is very good, in my experience I found that it wasn’t the best for my applications. One of the problems that I ran into was that the application loses focus while the function attempts to check for the Internet connection. To that extent, I present to you this alternative.
In addition, I’d like to add that this function is based on the comments made on this site by Jarek Gibek as well as the article ‘Get hostname and ip address of local computer(2)’ by Jaroslav Pisk.
How it Works
The way this function works is that it attempts to define which are the IP addresses which can automatically be excluded from consideration. Then it defines which IP addresses would signify that the computer is connected to the Internet. Here’s a sampling of IP addresses and what they mean to the function that should help to illustrate my point.
- 127.0.0.1 – localhost;
- Private Adress area(RFC 1597)
- 10.*.*.* – Class A;
- 172.16-31.*.* – Class B;
- 192.168.*.*– Class C;
- 169.254.*.* Microsoft AutoNet address area(See: http://lancanyon.com/autonet.htm for detail);
- Have you reason for other ranges exclusion?
The Function
While the function is stated (and commented) here, you can also download it below.
#include "winsock2.h"
BOOL IsInternetConnection()
{
char szHostName[128];
BOOL bPrivateAdr = false; // Private Address area
BOOL bClassA = false; // Class A definition
BOOL bClassB = false; // Class B definition
BOOL bClassC = false; // Class C definition
BOOL bAutoNet = false; // AutoNet definition
CString str;
if (gethostname(szHostName, 128) == 0 )
{
// Get host adresses
struct hostent * pHost;
int i;
UINT ipb;
pHost = gethostbyname(szHostName);
for (i = 0;
pHost!= NULL && pHost->h_addr_list[i]!= NULL;
i++ )
{
int j;
str="";
bClassA = bClassB = bClassC = false;
for( j = 0; j < pHost->h_length; j++ )
{
CString addr;
if( j > 0 ) str += ".";
ipb = (unsigned int)((unsigned char*)pHost->h_addr_list[i])[j];
// Define the IP range for exclusion
if(j==0)
{
if(bClassA = (ipb == 10)) break; // Class A defined
bClassB = (ipb == 172);
bClassC = (ipb == 192);
bAutoNet = (ipb == 169);
}
else if (j==1)
{
// Class B defined
if(bClassB = (bClassB && ipb >= 16 && ipb <= 31)) break;
// Class C defined
if(bClassC = (bClassC && ipb == 168)) break;
//AutoNet pasibility defined
if(bAutoNet = (bAutoNet && ipb == 254)) break;
}
addr.Format("%u", ipb );
str += addr;
}
// If any address of Private Address
// area has been found bPrivateAdr = true
bPrivateAdr = bPrivateAdr || bClassA || bClassB || bClassC;
// If any address of Internet Address area
// has been found returns TRUE
if (!bClassA
&& !bClassB
&& !bClassC
&& !bAutoNet
&& str != "127.0.0.1"
&& !str.IsEmpty())
return TRUE;
}
}
if (bPrivateAdr)
{
// The system has IP address from Private Address
// area,only. Internet from the computer can be accessable
// via Proxy. If user turn on proxy connection flag, the
// function believe Internet accessable.
return bProxyConnection;
}
return false;
}
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