由进程句柄ID如何得到窗户句柄ID?

struct EnumParam
{
 HWND hMainWnd;
 DWORD dwProcessID;
};

BOOL CALLBACK EnumWinProc(HWND hwnd, LPARAM lParam)
{
 DWORD dwID;

 EnumParam* pep = (EnumParam*)lParam;
 GetWindowThreadProcessId(hwnd, &dwID);

 if (dwID == pep->dwProcessID) {
  pep->hMainWnd = hwnd;
  return 0;
 }
 return TRUE;
}

void CPlayFlashDlg::Button3Click()
{
 EnumParam ep;
 STARTUPINFO si;
 PROCESS_INFORMATION pi;

 ep.hMainWnd = NULL;
 memset(&si, 0, sizeof(si));
 si.cb = sizeof(STARTUPINFO);
 if (CreateProcess(NULL,"notepad.exe c:\\1.txt",
  NULL,NULL,FALSE,0,NULL,NULL,&si,&pi))  
 {
  CloseHandle(pi.hThread);
  CloseHandle(pi.hProcess);

  ep.dwProcessID = pi.dwProcessId;
  EnumWindows((WNDENUMPROC)EnumWinProc, (long)&ep);
 }
 //此时的 ep.hMainWnd 就是你要的NodePad.exe窗口的句柄
}