Debugging

COM_INTERFACE_ENTRY_BREAK

Sometimes you need to debug your QueryInterface implementation. Maybe you're building a custom COM_MAP macro. Maybe you're seeing weird behavior on some interfaces. Sometimes the easiest way to track down a problem is in the debugger. This is where COM_INTERFACE_ENTRY_BREAK comes in:

#define COM_INTERFACE_ENTRY_BREAK(x) \
  { &_ATL_IIDOF(x), NULL, _Break },   

The _Break function outputs some helpful debugging information and calls DebugBreak:

static HRESULT WINAPI                                         
CComObjectRootbase::_Break(void*, REFIID iid, void**, DWORD) {
  (iid);                                                      
_ATLDUMPIID(iid, _T("Break due to QI for interface "), S_OK); 
  DebugBreak();                                               
  return S_FALSE;                                             
}                                                             

The call to DebugBreak is just like a breakpoint set in your debugger. It gives the active debugger the chance to take control of the process. When you're debugging, you can set other breakpoints and continue executing.