Internet Detection

Hi

I need to know if the computer is connected to the internet.
I'm using Windows calls like:     (FARPROC&)InetIsOffline = GetProcAddress(hURL, _T("InetIsOffline"));

This barely works. Most of the time when my wifi is turned off, or cable unplugged, it still says I'm connected.

Question: are there internet connection routines in the Toolkit? If so, are there examples?

Thanks!

I had the same problems, then I simply tried pinging google, which has proven to be enough in my case.

There's an "Event" SDK in windows from windows 2000 onwards that you can use to determine things like whether you have connectivity or not, and gives you indications when people log in or off, and power events (like going from utility to UPS power).

Other options are to do things like use IPHelper APIs to enumerate the system route table to see if you have a route to a host or not.

I presume you want something that won't

a) block
b) cause a dial

Cheers

Adrien

PPL1 wrote: I use this function, and it works fine:Public Declare Function InternetGetConnectedState Lib "wininet.dll" (ByRef dwFlags As Long, ByVal dwReserved As Long) As Long Public Function IsOnline() As Boolean  Dim LFlags As Long  IsOnline = InternetGetConnectedState(LFlags, 0&)End Function

I tried that, too.
But it's not always reliable.
The way I do it now is WSAStartup then gethostbyname and then WSACleanup

if ( InternetCheckConnection( "http://www.google.com", FLAG_ICC_FORCE_CONNECTION, 0 ) return TRUE;

this has worked for us without problems

 

terrym wrote: if ( InternetCheckConnection( "http://www.google.com", FLAG_ICC_FORCE_CONNECTION, 0 ) return TRUE; this has worked for us without problems

This indeed works, but requires Windows 2000 Professional or better.
If that's not important, then this is a good solution

Pinging Google is a very ugly solution. Imagine if all applications did this. Soon you end up with a DoS attack...

That was the problem here, we just needed to detect if we had a connection (a real connection) and this was the only reliable method we could find :(  if anybody knows of a better reliable method we will happily change our code :)

znakeeye wrote: #include <Wininet.h>   #pragma comment(lib, "wininet") BOOL isConnected = InternetGetConnectedState(INTERNET_CONNECTION_LAN | INTERNET_CONNECTION_MODEM, 0);

terrym wrote: znakeeye wrote: #include <Wininet.h>   #pragma comment(lib, "wininet")BOOL isConnected = InternetGetConnectedState(INTERNET_CONNECTION_LAN | INTERNET_CONNECTION_MODEM, 0);   Postitive we tried this, and the problem we found was if we disconnected the network cable it would still report as connected?

Same here.

You're right. "A return value of TRUE from InternetGetConnectedState indicates that at least one connection to the Internet is available. It does not guarantee that a connection to a specific host can be established."

znakeeye wrote: You're right. "A return value of TRUE from InternetGetConnectedState indicates that at least one connection to the Internet is available. It does not guarantee that a connection to a specific host can be established."   Have to do some research here. It seems odd that such a simple task is that hard...

znakeeye wrote: I believe this is the right way of doing this: InternetCheckConnection(NULL, FLAG_ICC_FORCE_CONNECTION, 0);   Who uses OS < Win2k??

How about this?

Hi

You might want to try GetAddrInfo() for several known hosts. This will avoid connecting to anything but the DNS server(s). Unfortunately, if the DNS server is on a local network system, or all addresses are cached (there or on your local system) it might give back a valid address even though outbound connections are down.

You might want to experiment with sending it invalid or reserved IPV4 addresses; these may force a connection to a real (external) DNS server, and the error returns may be different depending on the local system's (or local network's) actual connection to the internet. I haven't experimented with that.