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

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:
If both hwndParent and hwndChildAfter are NULL.
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")