m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME); 这句话作用是什么?对以后

m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME); 这句话作用是什么?对以后我程序编写有什么作用
CMyDlg::CMyDlg(CWnd* pParent /*=NULL*/)
:CDialog(CMyDlg::IDD,pParent)
{
//{{AFX_DATA_INIT(CMyDlg)
//}}AFX_DATA_INIT
// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);//获取图标句柄
memset(&mp.str,0,51);
n=0;
m=0;
}