Thread: close all

I'm trying to add a close all command to my text editor. I have tried putting the below code in the WndProc and MDIProc but nothing happens. Where does it go?

Code:

const char g_szChildClassName[] = "myMDIChildWindowClass";
case CM_CLOSEALL:
   {					
      HWND hwnd = FindWindow(g_szChildClassName,NULL);
      SendMessage(hwnd, WM_CLOSE, 0,0);
   }