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Check if online

Posted on 1997-12-07
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Last Modified: 2008-02-01
Is there some easy way to check if you are online from a program made in Visual C++?
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Question by:od0
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Expert Comment

by:chensu
ID: 1175064
You can use the Remote Access Service (RAS) function RasEnumConnections to check if there are any Dial-Up Networking connections.
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Author Comment

by:od0
ID: 1175065
Can you please specify how to use the RasEnumConnections command?
I can't make it work...
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Expert Comment

by:chensu
ID: 1175066
// return value of RAS functions
DWORD dwRet;

// get the number of connections
DWORD dwSizeBuf = 0, dwNumConnections = 0;
::RasEnumConnections(NULL, &dwSizeBuf, &dwNumConnections);

// enumerate the connections
if (dwNumConnections != 0)
{            
    // allocate the buffer
    LPBYTE lpbyBuf = new BYTE[dwSizeBuf];

    // enumerate the connections
    LPRASCONN lpConn = reinterpret_cast<LPRASCONN>(lpbyBuf);
    lpConn->dwSize = sizeof(RASCONN);
    if ((dwRet = ::RasEnumConnections(lpConn, &dwSizeBuf, &dwNumConnections)) != 0)
        // DISPLAYERROR(dwRet);
    else
        for (DWORD dwi = 0; dwi < dwNumConnections; dwi++)
        {
            // each connection handle is lpConn[dwi].hrasconn
        }

    // free the buffer
    delete []lpbyBuf;
}

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Author Comment

by:od0
ID: 1175067
Well, it still doesn't seems to work. When I compile my program I get a Linking error. It looks like this:
TestDlg.obj : error LNK2001: unresolved external symbol _RasGetConnectStatusA@8.
What am I doing wrong?
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Accepted Solution

by:
Tommy Hui earned 200 total points
ID: 1175068
You need to link with RASAPI32.LIB.
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Expert Comment

by:chensu
ID: 1175069
Yes, link with rasapi32.lib. (menu Project/Settings/Link)

Internet Shortcuts API in ActiveX SDK has a function.

InetIsOffline


BOOL InetIsOffline (
    DWORD dwFlags
);

Determines whether the system is connected to the Internet.

Returns TRUE if the local system in not currently connected to the Internet. Returns FALSE if the local system is connected to the Internet or if no attempt has yet been made to connect to the Internet.

dwFlags
Input flags for the function. This must be set to zero.
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Author Comment

by:od0
ID: 1175070
Greate! My online detector function is working just fine now. But I'm courious about the InetIsOffline() function. When I add that function to the code I am getting the same error as before, so I presume that I need to add a Library file. But which? The error looks like this:
TestDlg.obj : error LNK2001: unresolved external symbol "int __cdecl InetIsOffline(unsigned long)" (?InetIsOffline@@YAHK@Z)
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