How come FindWindow finds a window that EnumChildWindows doesn't?

Question

I'm looking for a window that its class name is "CLIPBRDWNDCLASS" (it can be found in office apps and other applications).

If I use FindWindow or FindWindowEx I find the first HWND that has this class, but I want all the windows with that class, so I decided to use recursive EnumChildWindows to enumerate all windows and find the window I want:

//-------------------------------------------------------------------------------
BOOL CALLBACK enum_wnd_proc(HWND h, LPARAM lp)
{
    char cls[1024] = {0};
    ::GetClassNameA(h, cls, 1024);

    if(std::string(cls) == "CLIPBRDWNDCLASS")
    {
        // match!
    }

    ::EnumChildWindows(h, enum_wnd_proc, NULL);

    return TRUE;
}
//-------------------------------------------------------------------------------
int _tmain(int argc, _TCHAR* argv[])
{
    ::EnumWindows(enum_wnd_proc, NULL); 
    return 0;
}
//-------------------------------------------------------------------------------

The this is that this window does not return by the EnumWindows, only by FindWindow.

Does anyone can tell why it doesn't work ???

Answer 1

The reason EnumWindows doesn't work is that the window you are looking for is a message only window.

FindWindowEx can find them in two cases:

1. If both hwndParent and hwndChildAfter are NULL.
2. If you specify 'HWND_MESSAGE' as your parent window.

This code will find all the relevant windows for you (a modified version of a solution from here):

HWND hWindow = FindWindowExA(HWND_MESSAGE, NULL, "CLIPBRDWNDCLASS", NULL);
while (hWindow )
{
    // Do something here with window...

    // Find next window
    hWindow = FindWindowExA(HWND_MESSAGE, hWindow , "CLIPBRDWNDCLASS", NULL);
}

Also note that unlike what's written in the above link, GetParent() for message only windows does not return HWND_MESSAGE (at least not for my tests).

Answer 2

My old easy way to ENUMERATE all message-only windows:

EnumChildWindows(GetAncestor(FindWindowEx(HWND_MESSAGE,0,0,0),GA_PARENT),addr EnumChildProc,0)

// GetAncestor(FindWindowEx(HWND_MESSAGE,0,0,0),GA_PARENT) = "GetMessageWindow" (class "Message")

// GetAncestor(FindWindowEx(HWND_DESKTOP,0,0,0),GA_PARENT) = GetDesktopWindow (class "#32769")