Is it possible to tell if WSAStartup has been call

问题:

I've started writing an ActiveX control that makes use of sockets.

Applications that use this control may or may not also use sockets. Is it possible for my control to tell whether WSAStartup has been called?

If not, call it. A little test reveals that calling WSAStartup multiple times is tollerated. But what happens if a different winsock version is requested? will this break other parts of the application?

回答1:

Yes it is possible.

And here is how it's done.

bool WinsockInitialized()
{
    SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (s == INVALID_SOCKET && WSAGetLastError() == WSANOTINITIALISED){
        return false;
    }

    closesocket(s)
    return true;
}

int main()
{
    //...
    if ( !WinsockInitialized() )
       // Init winsock here...

    // Carry on as normal.
    // ...         
}

But it's not really necessary to do this. It's quite safe to call WSAStartup at any time. It's also safe to end each successful call to WSAStartup() with a matching call to WSACleanup().

e.g.

// socket calls here would be an error, not initialized
WSAStartup(...)
// socket calls here OK

WSAStartup(...)
// more socket calls OK

WSACleanup()
// socket calls OK

WSACleanup()

// more socket calls error, not initialized

回答2:

• No, it is not possible to tell if WSAStartup() has already been called.

• Yes, WSAStartup() can be called multiple times in a single process, as long as the requested version is supported by the WinSock DLL. Calls to WSAStartup() and WSACleanup() must be balanced.

• WinSock initialization is a negotiated process; you are responsible for validating the info that WSAStartup() returns to make sure it meets your app's requirements.

• Existing sockets are not affected by subsequent WSAStartup() calls.

• Multiple sockets using different WinSock versions is allowed.

See the WSAStartup() documentation for more information.