VC++中的使用问题

char dot[1572864];  //1024*768*2
CBitmap bmp;        //内存位图
CDC wdc;            //设备环境      这几句在哪定义呀新手不懂帮帮忙
                                       下面的代码是可以在mainfrm.cpp中直接写上就行吗
                                       谢谢了
....
void CSurveillant_ServerView::OnIntitialUpdate()
{
..
static CWindowDC ddc(GetDesktopWindow());
pDC=&ddc;
wdc.CreateCompatibleDC(pDC);
bmp.CreateCompatibleBitmap(pDC,1024,768);
wdc.SelectObject(&bmp);
StaratServer();
}
void CSurveillant_ServerView::Ontimer(UINT nIDEvent)
{
wdc.BitBIt(0,0,1024,768,pDC,0,0,SRCCOPY);
..
}