//需要包含的头文件

include

//由CFrameWnd派生的CMyWnd类

class CMyWnd :public CFrameWnd

{
private:

char * ShowText;

public:

afx_msg void OnPaint();

afx_msg void OnLButtonDown(); //鼠标左键按下消息处理函数

DECLARE_MESSAGE_MAP( )

};
//消息映射的实现

BEGIN_MESSAGE_MAP(CMyWnd,CFrameWnd)

ON_WM_PAINT()

ON_WM_LBUTTONDOWN()

END_MESSAGE_MAP()

//WM_PAINT消息处理函数的实现

void CMyWnd::OnPaint()
{
CPaintDC dc(this);

dc.TextOut(20, 20, ShowText);

}
//WM_LBUTTONDOWMT消息处理函数的实现
void CMyWnd::OnLButtonDown()
{
ShowText ="有消息映射表的程序";
InvalidateRect(NULL, TRUE);
}
//程序员由CWinApp派生的应用程序类
class CMyApp:public CWinApp
{
public:

BOOL InitInstance();

};
BOOL CMyApp::InitInstance()
{

CMyWnd* pMainWnd = new CMyWnd;

pMainWnd->Create(0, L"MFC");

pMainWnd -> ShowWindow(m_nCmdShow); pMainWnd -> UpdateWindow();

m_pMainWnd = pMainWnd;

return TRUE;

}

//定义CMyApp的对象MyApp
CMyApp MyApp;

afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
感谢邀请，函数声明和实现里，把这两个参数加上