通过VC++ 新建一个MFC单文档应用程序，其工程名为mfcproject.新建后通过类视图可以看到一共有5个类：
CAboutDlg：对话框类，如关于对话框
CMainFrame：应用程序框架类，包括工具栏菜单等
CMfcprojectApp：应用程序类
CMfcprojectDoc：文档类
CMfcprojectView:也是和文档有关的视图类
1、mfcproject.cpp文件中定义了全局类 CMfcprojectApp theApp;在这个地方设置断点，调试运行可以发现整个程序首先执行到这个地方。
2、全局变量定义后将会调用CMfcprojectApp 类的构造函数
3、从mfcproject.h中可以发现 CMfcprojectApp继承自CWinApp类（在APPCORE.cpp中），根据继承性原理，程序将会首先调用CWinApp类的构造函数，如果细心地话会发现CWinApp的构造函数有参数，但CMfcprojectApp类构造函数并没有带参数，这是怎么回事呢？再仔细看下CWinApp类的构造函数：CWinApp(LPCTSTR lpszAppName = NULL); 看见了没这里的参数是默认值，这也就是为什么CMfcprojectApp构造函数没有带参数的缘故了
4、定义好全局变量以后，就要找主函数入口了，MFC程序的主函数入口为：
extern "C" int WINAPI
_tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
// call shared/exported WinMain
return AfxWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
}
该函数在APPMODUL.cpp中，从这个函数可以看出真正的入口函数应该为AfxWinMain（Winmain.cpp中）
int
AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPTSTR lpCmdLine, int nCmdShow)
{
ASSERT(hPrevInstance == NULL);
int nReturnCode = -1;
CWinThread* pThread = AfxGetThread();
CWinApp* pApp = AfxGetApp(); //获取子类
// AFX internal initialization
if (!AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow))
goto InitFailure;
// App global initializations (rare)
if (pApp != NULL && !pApp->InitApplication())
goto InitFailure;
// Perform specific initializations
if (!pThread->InitInstance()) //初始化注册窗口
{
if (pThread->m_pMainWnd != NULL)
{
TRACE0("Warning: Destroying non-NULL m_pMainWnd
");
pThread->m_pMainWnd->DestroyWindow();
}
nReturnCode = pThread->ExitInstance();
goto InitFailure;
}
nReturnCode = pThread->Run();
关键的语句是line8获取子类实例，line19初始化子类，完成窗口注册，line20可以在这些行上设置断点
5、 由于pThred当前指向子类，InitInstance函数是虚函数，因此 pThread->InitInstance()将调用子类的CMfcprojectApp::InitInstance()
InitFailure:
#ifdef _DEBUG
// Check for missing AfxLockTempMap calls
if (AfxGetModuleThreadState()->m_nTempMapLock != 0)
{
TRACE1("Warning: Temp map lock count non-zero (%ld). ",
AfxGetModuleThreadState()->m_nTempMapLock);
}
AfxLockTempMaps();
AfxUnlockTempMaps(-1);
#endif
AfxWinTerm();
return nReturnCode;
}
BOOL CMfcprojectApp::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.
CSingleDocTemplate* pDocTemplate;
pDocTemplate = new CSingleDocTemplate(
IDR_MAINFRAME,
RUNTIME_CLASS(CMfcprojectDoc),
RUNTIME_CLASS(CMainFrame), // main SDI frame window
RUNTIME_CLASS(CMfcprojectView));
AddDocTemplate(pDocTemplate);//新建一个单文档的模板，并将 doc，view，frame类添加到该模板中。
// Parse command line for standard shell commands, DDE, file open
CCommandLineInfo cmdInfo;
ParseCommandLine(cmdInfo);
// Dispatch commands specified on the command line
if (!ProcessShellCommand(cmdInfo))//窗口的注册（不太确定）
return FALSE;
// The one and only window has been initialized, so show and update it.
m_pMainWnd->ShowWindow(SW_SHOW);//显示窗口
m_pMainWnd->UpdateWindow();//更新窗口
return TRUE;
}
上述代码中红色部分是比较重要的地方，可以在这些地方设置断点。
6、窗口注册会调用函数BOOL AFXAPI AfxEndDeferRegisterClass(LONG fToRegister)在文件WINCORE.CPP中
7、紧接着调用BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)，创建窗口
BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
{
if( !CFrameWnd::PreCreateWindow(cs) )
return FALSE;
// TODO: Modify the Window class or styles here by modifying
// the CREATESTRUCT cs
//此处修改cs，实现用户自定义窗口
return TRUE;
}
8、接下来调用line3父类的precreatewindow函数
9、由于窗口包括frame框架类，因此需要调用cfrmwnd的create函数（WINFRM.cpp中），这个函数又会调用Cfrmwnd的父类CWnd::CreateEx函数
10、注册完窗口后就会执行消息响应，消息响应是通过 AfxWinMain中nReturnCode = pThread->Run()实现的
11、用一个dowhile循环实现消息循环 PumpMessage()
大概的MFC实现就写到这，可能有很多不对的地方，等熟悉以后再来更新！