采用多文档的默认Project，不改动代码，直接编译运行
会带有一个默认的子文档，
如何去掉，仅在“新建”和“打开”菜单后才出现子文档呢？
CxxxMDIApp类的InitInstance()在创建CMainFrame对象后调用CWinApp的ParseCommandLine()方法解析命令行参数，然后用ProcessShellCommand()方法处理命令行。对于空命令行，ParseCommandLine()方法将会生成一个FileNew命令，让ProcessShellCommand()方法调用CxxxMDIDoc的OnNewDocument()方法创建一个空文档。
为了避免创建空文档，一种可行的方法是修改InitInstance()来实现（字体加速的行）：
BOOL CxxxMDIApp::InitInstance()
{
...
if(cmdInfo.m_nShellCommand != CCommandLineInfo::FileNew)
{
if (!ProcessShellCommand(cmdInfo))
return FALSE;
}
...
}
下面是函数，我屏蔽了三句，也实现了没有初始文档
你看看，会不会有什么“后遗症”？
BOOL CExMultiApp::InitInstance()
{
AfxEnableControlContainer();
// Standard initialization
// If you are not using these features and wish to reduce the size
// of your final executable, you should remove from the following
// the specific initialization routines you do not need.
#ifdef _AFXDLL
Enable3dControls(); // Call this when using MFC in a shared DLL
#else
Enable3dControlsStatic(); // Call this when linking to MFC statically
#endif
// Change the registry key under which our settings are stored.
// TODO: You should modify this string to be something appropriate
// such as the name of your company or organization.
SetRegistryKey(_T("Local AppWizard-Generated Applications"));
LoadStdProfileSettings(); // Load standard INI file options (including MRU)
// Register the application’s document templates. Document templates
// serve as the connection between documents, frame windows and views.
CMultiDocTemplate* pDocTemplate;
pDocTemplate = new CMultiDocTemplate(
IDR_EXMULTTYPE,
RUNTIME_CLASS(CExMultiDoc),
RUNTIME_CLASS(CChildFrame), // custom MDI child frame
RUNTIME_CLASS(CExMultiView));
AddDocTemplate(pDocTemplate);
// create main MDI Frame window
CMainFrame* pMainFrame = new CMainFrame;
if (!pMainFrame->LoadFrame(IDR_MAINFRAME))
return FALSE;
m_pMainWnd = pMainFrame;
/********************************************************************
Writed by Nicholas.K.J
created: 2006/02/13
created: 13:2:2006 21:36
*********************************************************************/
// // Parse command line for standard shell commands, DDE, file open
// CCommandLineInfo cmdInfo;
// ParseCommandLine(cmdInfo);
//
// // Dispatch commands specified on the command line
// if (!ProcessShellCommand(cmdInfo))
// return FALSE;
//以上是我屏蔽屏蔽的地方，也是没有了初始文档
// The main window has been initialized, so show and update it.
pMainFrame->ShowWindow(m_nCmdShow);
pMainFrame->UpdateWindow();
return TRUE;
屏蔽是可以的，但此时程序不再处理命令行参数。当希望处理命令行参数的时候就需要自行编写代码处理。
还可以这样修改（加粗的部分）：
CCommandLineInfo cmdInfo;
cmdInfo.m_nShellCommand = CCommandLineInfo::FileNothing;
ParseCommandLine(cmdInfo);
由于对于空命令行，ParseCommandLine()不会修改cmdInfo，有效地阻止了在启动时新建文档。
当然还可以结合注册表来实现，例如在InitInstance()调用SetRegistryKey(_T("xxx"));之后，通过调用GetProfileInt()来读取注册表中的值（例如一个名为"NewDocOnStart"的DWORD值），如：
SetRegistryKey(_T("CompanyName"));
INT nNewDocOnStart = 0;
nNewDocOnStart = GetProfileInt(_T("ApplicationName"), _T("NewDocOnStart"), nNewDocOnStart);
然后在下面修改：
CCommandLineInfo cmdInfo;
cmdInfo.m_nShellCommand = nNewDocOnStart ？CCommandLineInfo::FileNew : CCommandLineInfo::FileNothing;
ParseCommandLine(cmdInfo);