In MFC, in wizard-generated WindowProc, how do I determine message sender window handle?

Question

I have a legacy MFC application originally written in Visual C++ 6. I need to do some minor changes to it but MFC is a black box to me.

There is this apparently wizard-generated function that processes messages

LRESULT CMainFrame::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
{
    // TODO: Add your specialized code here and/or call the base class

    switch (message)
    {
    case WM_CLOSE:
        ...;
  ...
  etc.
}

For some messages I need to get the sender window handle (which is from a different process). In Windows API a standard WindowProc has this handle as the first argument, but where is it in MFC?

Edit: Thank you Raymond and Mark. I see that I misunderstood how it works.

Answer 1

This information isn't available. The first parameter in a standard window procedure is the receiver, not the sender. This makes sense, too, since SendMessage and PostMessage identify the receiver by window handle. The sender, on the other hand, can be any thread, including a thread that doesn't own any windows.

If you need to identify the sender of a message in the code receiving a message you will have to explicitly pass an ID along. When crossing process boundaries you're going to have to marshal any referenced memory. The system won't do that for custom messages.